MUSCLES OF THE FEEDING APPARATUS,

Transcription

1 YI. STRUCTURE AND DISPOSITION OF THE MUSCLES OF THE FEEDING APPARATUS, AND ITS OPERATIVE EFFICIE-NCY

2 ?.Structure anj disposition The movements of the feeding apparatus are brought about by a series of actions of a number of muscles which together are responsible for the food manipu1ation.during the ingestion the food is handled by different snakes in different ways. For instance, some snakes squeeze the prey in between the body coils, kill, and then swallow. Some others immobilize the prey by injecting venom into the body of the prey by striking, and then swallow. Some other snakes are capable of swallowing the struggling prey alive. Since the feeding behaviour differs in different snakes, it is natural to expect that the muscles involved are variously disposed and adapted to bring about different movements of the jaw apparatus during food-cr~anoeuvring.a number of investigators have studied the disposition of the jaw-muscles with a view to correlating their structure 'with the operation for specific feeding habits in snakes. Cundall (1983). Cundall and Irish(l989) etc., have described the structure and function of the feeding apparatus during feeding in a few snakes. The disposition and the structure of the jaw-, hyoid- and tongue-muscles of'the three snakes under investigation have been studied here in detail with a view to finding out the variations,if any, and see whether they have any bearing on the

3 feeding behaviour. Based on main functions, the jaw-muscles of the feeding apparatus of snakes may be grouped as follows: I. fidductors of the lower jaw.t.a. M. Adductor mandibulae externus superficialis 1.b. M. Adductor mandibulae externus medialis 1.c. l.d. M. Adductor mandibulae externus profundus M. Adductor mandibulae posterior 1.e. N. Pseudotemporalis 2.Abductors of the lower jaw 2.a. 2.b. M. Depressor mandibulae anterior H. Depressor mandibulae posterior 3.Protractors of the upper jaw 3.a. M. Protractor pterygoidei 3.b. 3.c. M. Levator pterygoidei M. Protractor quadrati 4. Protractors of the lower law and retractors of the upper jaw 4.a. M. Pterygoideus 4.L. M. Pterygoideus accessories

4 5. Retractors of the unper jaw 5.a. 5.b. 5.c. 5.d. M. Retractor pterygoidei M. Retractor vomeris M. Cervico-mandibularis M. Neuro-mandibularis The nomenclature of the jaw-muscles followed in the present work is that of Kardong(l980). Since there is no uniformity in the nomenclature used by different authors while describing the muscle, synonyms of the muscles are also given here for ready reference. Nomenclature and synonymy - M. Adductor mandibulae externus superficialis M. Masseter-Hager (1906) M. Temporal anterieur-phisalix (1922) M. Capiti mandibularis superficialis-adams (1925) M. Adductor mandibulae externus superficialis. 1. acc-lakjer ( 1926) M. Masseter M.b.. Mi.Mii-Radovanovic' (1935) M. Adductor externus superficialis, Part 1. a-hass (1952) M. Adductor mandibulae externus pars anterior - Albright & Nelson ( 1959) M. Anterior temporal-parameswaran (1971)

5 M. Adductor esternus superficialis - Bhati 6 Dutta (1977) M. Adductor mandibulae esternus superficialis - Kardong (1980) M. Adductor externus superficial~s-biseswar (1981) M. Adductor externus superficialis-cundall (1986) - M. Adductor mandibu.j:ae externus medialis M. Temporalis - Hager (1906) M. Temporal noyen - Phisalix (1922) M. Capiti mandibularis medius - Adams (1925) N. Adductor mandibulae externus medialis - LaC:jer (1926) M. Temporalis medius - Radovanovic' (1935) M. Adductor externus medialis - Hass (1952) M. Adductor mandibulae externus pars media-allright 8 Nelson M. Middle temporal - Paremeswaran (1971) M. Adductor externus medialis - Bhati & Dutta (1977) M. edductor mandibulae externus medialis - Kardong (1980) M. Adductor externus medialis - Biseswar (1981) M. Adductor externus medialis - Cundall (1986) - M. Adductor mandihulae externus profundus ( 1959) M. Temporalis - Hager (1906) ' M. Temporal posterior - Phisalix (1922) M. Capiti mandibularis profundus - Adams (1925)

6 M. Adductor mandibulae externus profundus - LaC:jer (1926) M. Temporalis posterior - Radovanovic' (1935) M. Adductor externus profundus - Hass (1952) M. Adductor mandibulae externus, pars profundus - Albright & Nelson (1959) M. Posterior temporal - Parameswaran (1971) M. Adductor externus profundus - Bhati & Dutta (1977) M. Adductor mandibulae externus profundus - Kardong (1980) M. Adductor externus profundus - Biseswar (1981) M. Adductor externus profundus - Cundall (1986) - M. Adductor mandibulae oosterior Adductor rnandibulae posterior - L akjer (.1926) Posterior inferior - Radovanovic' (1926) Adductor posterior - Hass (1952) Adductor mandibulae medius, pars profundus - A lbright & Nelson ( 1959) Adductor posterior - Bhati & Dutta (1977) Adductor mandibulae posterior - Kardong (1980) Adductor posterior - Biseswar (1981) Adductor posterior - Cundall (1986) - M. Pseudotemporalis M. Pterygoparietalis - Hager (1906)

7 M. Parietomandibulair profunda - Phisalix (1922) M. Pterygoparietalis - Adams (1925) M. Pseudotemporalis - Lakjer (1926) M. Temporalis anterior - Radovanovic' (1935) M. Pseudotemporalis - Hass (1952) M. adductor mandibulae profundus - Albright & Nelson (1959) M. Pseudotemporalis - Rhati & Dutta (1977) M. Pseudotemporalis - Kardong (1980) M. Pseudotemporalis - Riseswar (1981) M. Pseudotemporalis - Cundall (1986) - M. Depressor mandibulae (anterior & posterior) M. Occipitoquadrato-mandiLularis - Hager (1906) M. Digastrique - Phisalix (1922) M. Occipitoquadratomandibularis (digastricus) - Radovanovicg M. Depressor mandibulae - Hass (1952) M. Occiyitoquadrato-mandibularls - Albright & Nelson (1959) M. Digastric (anterior and posterior) - Parameswaran (1971) ( 1935) M. Depressor mandibulae (portio anterior and portio posterior) Bhati & Dutta (q977) M. Depressor mandibulae (superficial and deep) (Occipito- - quadrate-mandibularis) - Kardong (1980)

8 M. Depressor mandibulae - Biseswar (198)) M. Depressor mandibulae - Cundall (1986) - M. Protractor ~teryuoidei Pterygo-sphenoidalis posterior -Hager (1906) ~. Sphenopterygoidien -Phisalix (1922') Pterygosphenoidalis posterior -4dams (1925) Protractor pterygoidei -Lakjer (1926) Pterygo-sphenoidalis posterior -Radovanovicq (1935) Protractor pterygoidei -Has5 (1952) Protractor ossis pterygoidei -4lLright 8 Nelson (1959) Sphenopterygoidien -Parameswaran (1971) Protractor pterygoidei -Rhati & Dutta (1977) Protractor pterygoidei -Kardong (1980) Protractor pterygoidei -Riseswar (1981) Protractor pterygoidei -Cundall (1986) Levator ~tervuoidei Post-orbito-pterygoidien -Phisalix (1922) M. Levator pterygoidei -Lakjer (1926) M. Pterygop<ietalis -RadovanovicV (1935) M. Levator pterygoidei -Hass (1952) M. Levator ossis pteryyoidei -Albr=ight 8 Nelson (1959) M. Post-orbitopterygoidien -Pararneswaran (1971) M. Levator pterygoidei -Bhati 8 Dutta (1977)

9 M. Levator pterygoidei -Kardong (1980) M. Levator pterygoidei -Biseswar (1981) M. Levator pterygoidei -Cundall (1986) - M. Protractor auadrati M. Sub-occipito-angular -Parameswaran (1971) M. Supraoccipito-quadrate-irtandibularis -Bhati & Dutta (1977) M. Protractor quadrarti -Kardong (1980) M. Protractor quadrati -Biseswar (1981) M. Protractor quadrati -Cundall (1986) Transversus-maxilli-pterygo-mandibularis-Her (1906) Pterygoidien externe-phisalix (1922) Pterygoideus anterior-adarns (1925) Pterygoideus-Lakjer (1926) Transverso-maxillo-pterygo-mandibularis (Pterygoideus)- Radovanovic'(l935) Pterygoideus-Hass (1952) Adductor mandibulae internus, pars anterior -Albright & Nelson (1959) Pterygoidien (external) -Parameswaran (1971) Pterygoideus (proper) -Bhati & Dutta (1977) M. Pterygoideus -Kardong (1980)

10 Pi: ~rygo-sphenoidal if ante t-i or --Haget- ( 1906) Cn!-,rnopalatine -Ph~.s~l ir. (.19?2) P1.e t-ygo-%pt,enoj.dal. i..3r,t e-jrr -fid?...ri,$ ( 1925) Rett-artor pterygoidei -I..l?Ljet-!.15.Zt) Pterygo-spttenoida1.i: anterior -Radovanovj.rv (1935! Retractor pterygoidej. -Has5!1952! Retractor ossjr pteryqoidej. -6ltright & Nelson V1959) Cphenopalatine -Fararneswat-an (197.i) Retractor pterygoidei -Rhati 8 Outta (1977) Retractor pterygoidei -Kardon~ ($980) Retractor pterygoidci -Ris,eswar (1951! Retractor pterygoidei -Cundall c.1956)

11 - M. Retractor vomeris M. Retractor vomeris -Kardong (1980) M. Retractor vomeris -Cundall (1986) Cervico-mandibularis -Hager (1906) Cervico-angulaire -Phisalix (1922) Depressor nandibulae -&dams (1925) Cervico-mandibularis -RadovanovicV (1935) Retractor quadrati -Hass (1952) Cervico-rnandibularis -AlLright & Nelson (1959) Cervico-maxillary -Paramesuaran (1971) Retractor quadrati -Rhati & Dutta (1977) Cervico-mandibularis -Kardong (1980) Retractor quadrati -Riseswat- (1981) Cervico-mandibularis -Cundall (1986) M. Neuro (vertebra) mandibulaire -Phisalix (1922) M. Neuro-costa mandibularis -Adam5 (1925) M. Neuro-mandibularis -tiass (1952) M. Neuro-costomandibularis -Albright & Nelson (1959). M. Vertebro mandibular -Parameswaran (1971)

12 M. Neuro-costomandibularis pars vertebralis -Rhati & Dutta ( 1977) M. Neuro-mandibularis -Kardong (1980) M. Neuro-costomandibularis -Rlseswar (1981) M. Neuro-costomandibularis (vertebral head) -Cundall (1986) The following is an a,ccount of the description of the Ophidian jaw-muscles based on their functions with special reference to the snal:es under present inve2stigation. 1. Adductors of the lower jaw 1.a. M, Adductor mandibulae externus su~erficialis The Adductor mandibulae externus superficialis (Plates- X,XI,XII) is visible in the anterior part of the head immediately after the removal of the skin. This parallel-fibred fleshy muscle takes its origin from the parletal and the posterior face of the prefrontal bone. It extends backwards and downwards to get insertion into the postero-ventral margin of the compound bone by an aponeurosis. From the point of origin the fibres run obliquely by passing below the quadrato-maxillary ligament. This muscle as it runs in a postero-ventral direction, covers the major part of the M. Adductor mandibulae externus medialis.

13 PLATE - X

14 PLATE - X Jaw-muscles of tropidonotus. Fig.1 Lateral view; Fig.2 Ventral view. Abbreviations : MAm - M. Adductor rnandibulae externus medialis; MAP - M. Adductor mandibulae externus profundus; MApo(is) - M. Adductor mandibulae posterior (inner slip); MApo(os) - M. Adductor rnandibulae posterior (outer slip): MAS - M. Adductor rnandibulae externus superficialis; MCm - M. Cervico-man$ibularis; MDa - M. Depressor mandihulae anterior; MDp - M. Depressor mandibulae posterior: MLpt - M. Levator pterygoidei: MNm - M. Neuro-mandibularis: MPpt - M. Protractor pterygoidei: MPq - M. Protractor quadrati: MPst - M. Pseudotemporalis: Mpt - M. Pterygoideus; MPtac - M. Pterygoideus accessories; MRpt - M. Retractor pterygoidei; MRv - M. Retractor vomeris; Qml - Quadrato-maxillary ligament.

15 PLATE- x

16

17 PLATE - XI Jaw-muscles of ratsnake. Fig.1 Lateral view; Fig.2 Ventral view. Abbreviations : MAm - M. Adductor mandibulae externus medialis; MAp - M. Adductor mandibulae externus profundus: MApo(is) - M. Adductor mandihulae posterior (inner slip); MApo(os) - M. Adductor mandibulae posterior (outer slip); MAS - M. Adductor mandibulae externus superficialis; MCm - M. Cervico-mandibularis; MDa - M. Depressor rnandibulae anterior; MDp - M. Depressor mandibulae posterior; MLpt - M. Levator pterygoidei; MNm - M. Neuro-mandibularis: MPpt - M. Protractor pterygoidei; MPq - M. Protractor quadrati: MPsf - M. Pseudotemporalis; Mpt - M. Pterygoideus; MPtac - M. Pterygoideus accessories: MRpt - M. Retractor pterygoidei; MRv - M. Retractor vomeris: Qml - Quadrate-maxillary ligament.

18

19 PLATE - XI1

20 PLATE - X I 1 Jaw-muscles of cobra. Fig. I Lateral. view: Fig.2 Ventral view. Abbreviations : MAVI - M. Adductor ntandihulae externus wedialis; MAp - M. Adductor mandibulae externus profundus; MAp(ap) - M. Adductor rrlandibulae externus profundus (anterj.or portion); MAp(pp) - M. Adductor mandibulae e::ternus profundus(posterior portiont: MApo(is) - M. Adductor mandibulae posterior (inner slip); MApo(os) - M. Adductor n~andibulae posterior (outer slip); MAS - M. Adductor rnandibu!se externus superficialis; MCm - M. Cervico-mandibularis; MDa - M. Depressor mandibulae anterior; MDp - M. Depressor mandibulae posterior; MLpt - M. Levator pterygoidei; MNm - M.Neuro-mandibularis; MPpt - M. Protractor pterygoidei; MPq - M. Protractor quadrati; MPst - M. Pseudotemporalis: Mpt - M. Pterygoideus; MPtac - M. Pterygoideus accessories; MRpt - M. Retractor pterygoidei; MRv - M. Retractor vomeris; Qml - Quadrats-maxillary ligament; Vg - Venom gland.

21 - HP;i Fig 2

22 PLATE - XI11

23 PLATE - XI11 Nerve supply to the jaw-muscles of tropidonotus (Fig.?). ratsnake (Fig.21 and cobra (Fig:3). Abbreviations : Cn - Cranial nerve XII; Fn - Facial nerve VII; Tgn - Trigerninal nerve V; N~K, - Nerve to M. Adductor mandibulae externus medialis: NAp - Nerve to M. Adductor mandibulae externus profundus: NAp(ap) - Nerve to M. Adductor rnandibulae externus profundus (anterior portion); NAp(pp) - Nerve to M. Adductor mandibulae externus profundus (posterior portionl; NApo(is) - Nerve to M. Adductor mandibulae posterior (i.nner slip); NApo(os) - Nerve to M. Adductor mandibulae posterior (outer slip); NAs - Nerve to M. L \ Adductor mandibulae externus superficialis; NCm - Nerve to N. Cervico-mandibularis: NDa - Nerve to N. Depressor mandibulae anterior: NDp - Nerve to M. Depressor mandibulae posterior; NLpt - Nerve to M. Levator pterygoidei; NNm - Nerve to M. Neuro-mandibularis; NPpt - Nerve to M. Protractor pterygoidei; NPq - Nerve to M. Protractor quadrati: NPst - Nerve to M. Pseudotemporalis; NPt - Nerve to M. Pterygoideus; NPtac - Nerve to M. Pterygoideus accessories: NRpt - Nerve to M. Retractor pterygoidei: NRv - Nerve to M. Retractor vomeris; NVg - Nerve to venom gland.

24

25 ' The disposition of the above muscle is more or less similar in tropidonotus and ratsnal::e. However, the M. Adductor rnandibulae externus superficialis of cobra differs from that of tropidonotus and ratsnake. This muscle is divisible into vertical and horizontal sets. The ventral set arises from the parietal and the posterior face of the postfrontal and runs downwards. Most of the fibres insert into the dorso-medial surface of the posterior region of the venom gland. The horizontal set arises from the postero-dorsal projection of the maxilla by means of postorbital maxillary ligament. The fibres run posteriorwards in close association with the dorsal surface of the capsule of the venom gland. These fibres unite with the remaining fibres which arises from the parietal and postfrontal, and some of the merged fibres insert into the posterior corner of the venom gland. The rest of the fibres move downwards, medial to the venom gland, and insert on the ventro-lateral aspect of the mid-region of the mandible. The M. Adductor mandibulae externus superficialis is innervated by the trigekinal. nerve (V) (Plate-XIII). The function of this muscle is the adduction of the mandible. In cobra, it also acts as a compressor of the venom gland.

26 1.b. II, Adductor mandibulae externus medial16 (Plates-X,XI,X11) This muscle is situated behind the M. Adductor mandibulae externus superficialis. It is a parallel-fibred vertical muscle which taites a fleshy origin from the parieto-supratemporal region of the cranium. The muscle bundle extends downwards,.becomes narrow, and inserts directly on the compound bone just anterior to the Meckelian cavity. The above description stands more or less good for all the three different snakes studied here. The N. Adductor mandibulae externus rnedialis is innervated by the trigeminal nerve (V) (Plate-XIII). This rriuscle functions in pulling the lower jaw (adduction) towards the supratemporal. I. c., Adductor mandibulae externus profundus This is a large triangular block of parallel-fibred muscle seen posterior to the M. Adductor mandibulae externus medialis. It takes a fleshy origin in the entire outer lateral side of the quadrate.' The muscle moves downwards and inserts directly into a low depression which covers almost the whole of the postero- lateral surface of the compound Lone. This muscle is covered exter-pally with the quadrate-maxillary ligament. In tropidonotus

27 and ratsnake, the disposition is almost same. However, in cobra,the muscle is divisible into anterior and posterior parts. The anterior part takes its origin in the lateral antero-dorsa' corner of the quadrate. The posterior part originates beneath the origin of the anterior part,and extends to the entire length of the lateral side of the quadrate.hoth the parts unite to form a large thick muscle as it runs downwards and inserts into the depression on the posterdateral side of the compound bone. The M.Adductor mandibulae externus profundus is innervated by the trigeminal nerve (V). (Plate-XIII). quadrate. This muscle functions in drawing the mandihle towards the 1.d. M.Adductor mandibulae ~osterior (Plates-X,XI,XII) This is a triangular block of muscle composed of parallelfibres, concealed beneath the M.Adductor mandibulae externus profundus.the M.Adductor mandibulae posterior takes a fleshy origin in the antero-medial side of the quadrate, and extends downwards. The muscle is divided into two slips, an inner and an outer, by the prearticular crest of the mandible. The outer slip is inserted into the Meckelian canal, and the innelslip is i.r.ser,ted into the inner lateral side of the prearticular 'crest.

28 The disposition of the muscle is more or less same in the three different snakes studied here. The trigeminal nerve(v) innervates this muscle (Plate-XIII). The function of the M. Adductor n~andibulae posterior is to draw the mandible towards the quadrate. M. Pseudotemporalis is a parallel-fibred ribbon-like muscle arising from the parieta1,just behind the origin of the M.Adductor mandibulae externus superficialis. The major part of this muscle is covered by the fibres of M.Adductor mandibulae externus medialis. The M.Pseudoternporalis extends posteroventrally and inserts directly into the compound bone just anterior to the insertion of the M.Adtluctor rnandibulae externus medialis. The M. Pseudotemporalis lies lateral to the M-Levator pterygoidei and M.'~ter~goideus. The description is more or less good for tropidonotus, ratsnake and cobra.. The M. Pseudotemporalis is innervated by the trigeminal nerve (V) (Plate-XIII). his muscle serves to adduct the mandible.

29 2. fibductors of the lowet- jag 2.a. M.Depressor mandibulae anterior (Plates-X,XI,X11) This 'parallel-fibred n~uscle lies just behind the M.fidductor rnandibulae externus profundus.lt takes a fleshy origin in the whole length of the posterior projection on the upper region of the quadrate. This muscle extends downwards and backwards on the outer surface of the quadrate, and inserts directly into the dorsal surface of the retroarticular process of the mandible. The above-mentioned description holds good for the muscles of the three different snakes under investigation. This rrluscle is innervated by the facial nerve (VII) (Plate-XIII). The function of M. Depressor mandibulae anterior is to open the mouth by pulling the retroarticular process upward. 2.b. M, Decmressor ntandibulae ~osterior (Plates-X, XI, X I I ) The M. Depressor mandibulae posterior is also a parallelflbred muscle which arises by a nairow tendon from the skull-roof just anterior to the origin of the M. Depressor mandibulae anterior. The M. Depressor rnandibulae anterior and posterior are separated by the M. Cervico-quadratus, which passes between the two. The M. Depressor mandibulae posterior is

30 comparatively smaller than the anterior muscle. This muscle also extends bacl::wards and downwards, on the outer surface of the quadrate,and lies side by side to the anterior muscle. Then it gets inserted directly into the retroarticular process of the mandible. The disposition of the above-mentioned muscle is more or less same in tropidonotus, racsnake and cobra. The M. Depressor mandibulae posterior is innervated by the facial nerve (VII) (Plate-XIII). This muscle serves to open the mouth by pulling the retroarticular process upward. 3. Protractors of the upper jaw 3.a. M, Protractor ptervqoidei (Plates-X, XI, XII) This is a parallel-fiqred, strong and long muscle which takes a fleshy origin in the ventral surface of the sphenoid complex. It passes obliquely outwards and posteriorwards along the floor of the braincase. It becomes fusiform in shape, and inserts into the postero-dorsal end of the pterygoid with an especially firm attachment to the caudal tip of the bone. The disposition is more or less sis~ilar in the three different snakes here studied.

31 This muscle is innervated by the trigeminal nerve (V) (Plate-XIII). The M. Protractor pterygoidei serves to protract the palato- pterygoid bar. 3.b; M, Levator ptervooidei (Plates-X,XI, XII) The M. Levator ptersgoidei is parallel-f ibred, long and powerful. It takes a fleshy origin in the ventro-lateral side of the parietal, behind the postf rontal bone. It passes ventrally, widening along an anterior-posterior axis to give a long fleshy insertion into the dorso-lateral side of the pterygoid up to ectopterygoid-pterygoid articulation. This muscle lies rather deep in the palatal surface of the head. The above-mentioned description holds good for tropidonotus, ratsnake and cobra. The M. Levator pterygoidei is innervated by the trigeainal nerve (V) (Plate-XIII). The function of this muscle is to protract the palato- pterygoid bar during feeding. 3.c. Protractor quadrati (Plates-X,XI,XII) This flat, parallel-fibred, and roughly triangular muscle originates from a tendon from the mid-ventral side of the

32 basioccipital. It runs towards the quadrato-mandibular articulation. The muscle inserts on the quadrate and the retroarticular process of the mandible. In tropidonotus, ratsnake and cobra, the disposition of the above-mentioned muscle is more or less similar. The M.Protractor quadrati is innervated by the trigerr~inal nerve (V) (Plate-XIII). The muscle serves to protract the quadrate-m~andibular articulation, which results in the protraction of all the bones related to it. 4. Protractors of the lower jaw and retractors, of the udder law This is a long, parallel-fibred and stout muscle which takes its origin in the lateral maxillary process of the ectopterygoid primarily by a prominent tendon. This tendon remains superficialrand passes ventrally,reachjng the middle region of the muscle. A few fibres of this muscle also arise from a small area on the ectopterygoid immediately medial to the origln of the tendon. The fibres extend backward,and reach the quadrato- mandibular articulation. The fibres form a swollen belly in this region which projects below the compound bone. The fibres curve

33 upwards and get inserted into the ventral surface of the retroarticular process of the compound bone. The above description stands more or less good for tropidonotus. ratsnake and cobra. However, a few fibres of this muscle are attached to the venom gland, in cobra. The Pl.~te!$oideus is innervated ty the trigeminal nerve (V) (Plate-XIII). This rr~uscle has two functions. It serves to protract the mandible, and to retract the palato-maxillary arct1,during feeding. 4.b. M, Pteryaoideus accessories (Plates-X,XI,XII) The H. Pterygoideus accessories is a parallel-fibred, broad and strong muscle with a fleshy origin in the ventral surface of the postero-lateral part of the pterygoid. The origin estends the base of ectopterygoid. - to As it extends back:wards, its fibres converge and insert into the inner side of the retroarticular process of the mandible, along with the insertion of the N. Pterygoideus. In tropidonotus, ratsnake and colra, the disposition of the muscle is more or less similar. The trigeminal nerve(v) innervates the M.Pterygoideus accessories.

34 This n~uscle serves to protract the mandible and retract the palato-pterygoid bar,during swallowing process. 5. Retractors of the upper jaw 5.a. M, Retractor ptervqoide~. (Plates-X, XI, XII) The M.Retractor pterygoidei is a parallel-fibred, short and massive muscle situated on the palatal surface. It takes a fleshy origin in the sphenoid com~plex,at the ventla1 surface of the braincase anterior to the origin of M. Protractor pterygoidei. It passes forward and inserts into the anterodorsal surface of the pterygoid and the postero-dorsal surface of the palatine. The structure of the above-mentioned muscle is more or less same in the three different snakes under investigation. The trigeminal nerve(v) innervates this muscle. The M. Retractor pterygoidei functions so as to retract the palato-pterygoid bar. 5.b. M, Retractor vomeris This is a small, parallel-fibred and spindle-shaped muscle which arises from the sphenoid just anterior to the origin of M. Retractor pterygoidei. As it passes forward, the fibres converge

35 into a narrow tendon that accounts for half of the total muscle length, and runs forward again gaining insertion into the postero-dorsal edge of the vomer. The M. Retractor vomeris is covered laterally by the M. Retractor pterygoddei. In tropidonotus, ratsnake and cobra, the structure of the M.Retractor vomeris is more'or less similar. XIII). This muscle is innervated by the trigeminal nerve(v) (Plate- The function of M. Retractor vomeris is the retraction of the snout complex. 5.c. & Cervico-nandibularis (Plates-X, XI, X11) This is a parallel-filred, thin, muscular sheath with a fleshy origin in the epimysium of the spinalis--semispinalis comp1e:c near the dorsal midline of the cervical region. It runs in an antero-ventral direct-ion, passing over the M. Cervico- quadratus, and narrowing so as to insert into the lateral aspect of the quadrato-mandibular articulation adjacent to the origin of the quadrato-ma~illary ligament. The above description stands good for tropidonotus, ratsnake and cobra. The M. Cervico-mandibularis is innervated by the facial nerve (VII) (Plate-XIII).

36 This muscle serves to draw the quadrato-mandibular articulation backward, which causes the retraction of all the bones related to it. The M. Neuro-mandibularis is a parallel-fibred muscle, with a fleshy origin in the epimysium of the spinalis-semispinalis muscles, posterior to the origin of M. Cervico-mandibularis. It extends obliquely forwards, along the posterior border of the M. Cervico-mandibularis, and joins with some of the fibres of throat musculature. The muscle runs further anteriorly and inserts into the latero-ventral surface of the rnandi ble by an aponeurosis, near the dentary. Except for sorrte structural differences in the throat muscle fibres which are attached to the anterior part of the M. Neuro-mandibularis, the disposition of the M. Neuromandibularis is more or less same in tropidonotus, ratsnake and cobra. Cranial nerve XI1 innervates the M. Neuro-mandibularis. This muscle serves to draw back the quadrate-mandibular articulation, via the mandible whikh causes the retraction of all bones related to it.

37 (1977). The nomenclature followed here is that of Hhati and Dutta a. Hvoid-rrtuscles (Plate-XIV) I. M, Neuro-costo mandibularis hvoideus This is a parallel-fibred muscle originating from the compound bon'e immediately after the insertion of the M. Neuromandibularis. It extends posteriorwards and inserts into the anterior region of the hyoid. 2. M, Geniohvoideus This is a broad and parallel-fibred muscle, arising from the ventral mesial border of the compound bone just posterior to the origin of the M. Intermandibularis. The M. Geniohyoideus extends mesialwards and inserts into the lateral border of the processus entoglossus and the basihyoid. 3. M, Omnohvoideus This parallel-fibred muscle originates from the skin in the neck region. It runs obliquely mesialwards and inserts into the anterior ventro-lateral part of the basihyoid. The M. Omnohyoideus lies below the N. Neuro-mandibularis.

38 PLATE - XIV

39 PLATE - XIV Diagrammatic representation of the snake-hyoid muscles and tongue-muscles. Abbreviations : Hpd - Hyoid: M.Gg - M. Genioglossus; MGh - M. Geniohyoideus: MHg - M. Hyoglossus: MHt - M. Hyotrachealis; MIm - M. Inter-mandibularis: M Mhapro - M. Mflohyoldeus anterior profundus: M Mt - M.Mandibulo-tracheal15; M Ncmh - M.Neuro-costo * mandibularis pars hyoideus; M Nm - M. Neuro-mandibularis; M Oh - M. Omnohyoideus: Msh - M. Sternohyoideus: M. Sth - M. Sternothyroideus; Tgs - Tongue-sheath; Tr - Trachea.

40

41 4. t?, Sternohvoideus This muscle is a parallel-f ibred one, which also originates from the skin of the neck region just posterior to the origin of the M. Omnohyoideus. It estends mesialwards along with the M. Omnohyoideus and inserts into the ventro-lateral border of the basihyoid just posterior to the insertion of the M. Omnohyoideus. 5. t?, Sternothvroideus The M. Sternothyroideus is a parallel-fibred m~uscle which lies between the tongue-sheath and the basihyoid. This is a small muscle which arises from the scin in the neck region. It extends forwards, aln~ost parallel to the mid-longitudinal axis, and inserts into the inner Lorder of the basihyoid. The insertion of the M. Sternothyroideus is almost opposite to that of the insertion of the M. Neuro-costo mandibularis pars hyoideus. The hyoid-n~uscles do not serve in the protraction or retraction of the tongue in (Smith and Mackay. 1990) the three different snakes studied 'ere. The structural variatlons of the hyoid-muscles among the snakes under study are not mentioned here because these muscles do not serve to protract or retract the tongue.

42 1. M, Hvoalossus The paired ttyoglossus muscles share the major part of the tongue musculature. In addition to the Hyoglossus muscles, the tongue carries dorsal longitudinal bundles. Some perpendicular bundles are also present which run perpendicular to the long axis of the tongue. The Hyoglossus muscle originates from, the posterior end of the ceratobranchial cartilage and extends forwards parallel to each other so as to lie beside its fellow on the other side. They are enclosed in a thick covering of connective tissue, i.e., the tongue-sheath. The contraction of the perpendicular bundles causes the protraction of the tongue, and the contraction of longitudinal bundles, mainly in the M. Hyoglossus, causes the retraction of the tongue (Smith and Kier, 1989; Smith and Mackay, 1990). 2. M, Genioalossus The M. Genioglossus is a paired, parallel-fibred and long muscle. This muscle originates from two heads anteriorly, from the tip of the lower jaw. One head arises from the anterior tip of the mandible, and the other arises just behind the former. The two heads unite, become stout,. and run posteriorwards

43 parallel to the tongue-sheath. It inserts on the fascia of the Hyoglossus muscle. This muscle serves only to bucl::l.e the tongue (Smith and Kier, 1989; Smith and Mack:ay. 1990). The structure of the tongue-muscles show very much variations in the arrangement of the muscle fibres anlong the three different snakes studied here.. However, the structural variations are not mentioned here because the tounye-muscles do not serve the manipulation of food in snakes. 11 Operative 'efficiency of the feedinn] arnparatus As already mentioned in the introductory chapter, the operative efficiency of the feeding apparatus depends on a number of factors. Of these, the din~ensional variations of the bony elements of the skull, and the structure and disposition of jawmuscles have already been noted earlier. The operational efficiency of the lever systems has been worked out with reference to: C l ) Lever systems of the feeding apparatus, and (2) Quantitative myology. I. Lever systems of the feedinu a~lparatus In bringing out various movements, the quadrato- supratemporal articulation, the quadrate bone, the quadrato-

44 mandibular articulation and the fronto-nasal hinge, play n~ajor roles. A. Abduction (Plate-IV, Fig.,I) This involves a first-class lever system. The articulation of the rr~andible with the quadrate forms the pivot (P) on which the lever works. The abductor muscles are inserted into the retroarticular process, which is situated posterior to the pivot. The distance between the insertion of the muscle into the retroarticular process and the pivot forms the force arm (d ). 2 The distance from the pivot to the symphysis of the mandible constitutes the work arm (L). The contraction of the abductor muscles briny about the opening of the jaw, by lowering the work: arm on its pivot. B. Adduction (Plate-IV, Fig.,I) The adduction involves the operation of a simple third-class lever system.here the quadrato-mandibular articdlation forms the pivot(p). The add4tor muscles insert into the lower jaw between the pivot and the point of symphysis. The distance from the insertion of the rrtuscle into the rrtandible to pivot constitutes the force arm (d). The distance from the pivot(p1 to the symphysis of the mandible forms the work arm (L). Owing to the

45 contractions of the adductor muscles, the lower jaw is pulled upwards on its pivot. C. Protraction The protraction of the upper jaw involves a complex first- class Lever system in the case of M. Protractor pterygoidei and M. Levator pterygoidei. But in the case of fl. Protractor quadrati, the lever system involved is a simple second-class. In the forrr~er case, fronto-nasal hinge forms the pivot (P ). The 2 protractor muscles are inserted into the palato-pterygoid bar. The longitudinal axis of this bar is in exact direction of the force acting on the power arm. The perpendicular distance between the fronto-nasal hinge and the palato-pterygoid bar constitutes the force arm (R). The distance from the pivot (P ) 2 to the tip of the snout forms the work arm (L ). Owing to the 2 contraction of the protractor muscles, the palato-pterygoid bar is pulled forward resulting in the protraction of all the upper- jaw elements. In the latter case, the M. Protractor quadrati is inserted into the tip of the force arm (L ), the quadrate. The 3 quadrato-supratemporal articulation forms the pivot (P ). Here 3 - work: arm (R ) is equal to the force arm, i.e., the force arm and 3 work arm are the length of the quadrate. The contraction of the M. Protractor quadrati results in the movement of the quadrato-

46 n~andibular articulation forward, which protracts all the upper- jaw elements due to the. connection Of the pterygoid with the quadrato-mandibular articulation. The protraction of the lower jaw involves a simple second- class lever system. The quadrato-supratemporal articulation forms the pivot (P ). The muscles are inserted into the tip of 3 the force arm (L ) which is the distance between the pivot (P ) 3 3 and the quadrato-mandilular articulation. Work arm (R ) is also 3 - considered to have the same length as that of the force arm. The muscle contraction results in the protraction of the lower jaw. E. Retraction The retraction of the upper jaw involves a cornple:.: first- class lever except in the case of N. Cervico-rnandiLularis. When considering the n~uscles, viz., N. Pterygoideus. M. accessories, M. Retractor vomeris and M. Retractor Pterygoideus pterygoidei, the fronto-nasal hinge forms the pivot (P ). The Palato- 2 pterygoid bar gives the Lase for the insertion of the muscles. The longitudinal axis of this bar is in exact direction of the force acting on the power arm. The perpendicular distance from the fronto-nasal hinge (P ) to the palato-yterygoid bar 2 constitutes the force arm (R). The work arm (L ) forms the 2 distance between the fronto-nasal hinge and the tip of the snout.

47 The contraction of the above-mentioned muscles draws the palato- pterygoid bar baclrwards which results in the rnoverr~ent of all the upper-jaw elements in backward direction. In the case of M. Neuro-mandibularis, the quadrato- supratemporal articulation forms the pivot (P ). The muscle is 3 inserted into the mandible, the longitudinal axis of the same is in exact direction of the force acting on the power arm. The perpendicular distance between the pivot (P ) and the mandible is 3 considered as the force arm (R ). The distance between the pivot 2 (P ) and the quadrate-mandibular articulation forms the work arm 3 ~- (L ). Owing to the contraction of the muscle, the force is 3 transmitted to the quadrate-mandibular articulation through mandible, which results in the back:ward movement of the same. The quadrate-mandibular articulation is connected with the pterygoid and the maxilla with lin~aments. So the movement the is transmitted to the pterygoid and ma?:illa which results in the retraction of.al1 upper-jaw elements. A simple second-class lever system is involved in the case of the M. Cervico-mandibularis. Here also the pivot (P ) is the 3 quadrato-supratemporal articulation. The distance between the pivot (P ) and the quadrate-mandibular articulation to which the 3 rrtuscle is attached, forms the force arm (R ). The same is 3

48 considered as the work: arm (L ). The contraction of the M. 3 Cervico-mandibularis pulls the lquadrato-mandibular articulation backwards, resulting in the movement of all upper-jaw elements in the same direction. 2. Quantitative myoloqy A study of the effective forces and their indices calculated during the present investigation is given in the followin'g talles ( I X to XXXII):

49 tffectivf FORCE Of ADDUCTION BY THE n. 400UCTOR MNDIBULAf 4lTERNUS GUP~RfICIkLIS Snake No. of f o e f SinLfd Length of Moment Length Index to the speciaen Average the force of torque of the efftctive weight of arn 'dvam 'TI gm na work arn force nuscle in 91 L a 't' gn... Tropida notus Cabra TABLE X IfftCTlVE forct OF kqouction BY THE I(- LODUCTOR MAMDIBULht [XTERWUS MEOIRLIS Snake Na. of force f SinLfd Length sf loatnt Lcngth Index to the 5peciaen lvtrage the farce af tarsue at the effective #tight of arm 'd'am 'T' go am work ira force autcle in gm 'Lv a# 'tl #m... Cobra

50 TABLE XI EFFECTIVE FORCE Of ADDUCTION BY THE I. ADDUCTOR MANDlBULAE EXTERNUS PROfUNDUS Snake No. of F o e F Sin.LFd Length of tlonent Length Ir~dex to the specinen Average the forte of torque of the tffectivc weight of arm 'd'nn '1' gr nr work arn force nuscle in gn '1' an 'tg gn Tropido notui 'TbBLE xn IFFfCTIYE lorce BY THE A, ADDUCTOR IANDIBULAE POSTERIOR (ASDUCTI~) Snake Wo. of o r F SinLFd Length of Horcnt Length Index to the 5pecinen Average the force of torque of the effective weight of arn 'dtn '1' ga am work are force nurtle in gn. - L r... 't' gr Tropido notus Cobra

51 TABLE X l l l EfIECTIVE IORCE OF ADDUCTION BY THE I. PSEUDOTEAPORILIS * Snake No. of force 'f' SinLId Length of lorent Length Index to the ~peciren Average the force of torque of the effective weight of arr 'd'ro '1' pr ar work an force ruscle in gm '1 n 't' gr * Tropido notus Cobra ' TABLE 1lY EIFtCTlYE IORCt Of ABDUCTION RY THE I. OElRESSOR HANDIBULAE ANTERIOR Snake No. of force 'I' Sin~fdz Length of Iorent Length Index to the sgeciren Average tbe fort@ of torque of tht effective weight of are 'd~'n/tf g am work arr force ruscle in go. '1 r 't' ga Cobra *

52 IFftCTIVI FORCE Of ABDUCTION BY THI A. OIPRESSOR AANDIBULAE POSTtRIOR * * Snake No. of Foe 'f.sinlfd2 Ltngth of Uoatnt Length Index to the spetiren Average the fortc of torque of the effective weight of a ' a n '1' gr an work are forte austle in fa 1... 't' gm Ratrnake , Cobra TABLE XVl IFFECTIVI forcl Of PROTRACTION (UPPER JAW) BY THE U. PROTRACTOR PTlRVGOIDIl Snake No. of fortr 'F' C o s ~ r Length of Uoaent Length Index to the speci~en Average the force of torque of the effective weight of arn :Rqra 'TI gr I@ work an forte eustle in gn 12 a*... 't' gr Ratsnake , Cobra

53 TABLE XYIl EFFECTIYF FORCE Of PROTRACTION (UPPFR JAU) BY THI I. LEYATOR PTERYCOIDEI Snakr No. of f~rce 'ft COIL; Length af lolent Length Index to the syecireo Average the force of torque of the effectivt weight of a n 'R'ma '7' gn m work arm force nuscle in gm L?4n 'ttgn * * Tropido notur Cobra IfFECTIVt FORCE OF PROTRACTlON (UPPER JAU) BY THE II. PROTRACTOR QUADRAT1... Snake No. of f o r f SinLfR; Length of llo~tnt Length Index to the specinen Average the force af torque of the efftrtive weight of arn 'R3'n 'T' qa nn work arr farce auscle in ge L3 n 't' pn Tropido notus Cobra H

54 ... Snake No. of f o e F SinLFR; Length of Worent Length Index to the sgetiren Averagc the force of torque of the effective weight of a a 'Tt ga ra work ara farce auscle in ga Law... 't'ga Tropido aotus Cobra TABLE XX IfFtCTIVE FORCl OF PROTRACTlON (LOYtR JAN) BY THE I. PTtRYGOlDEUS lccessories * Snake Yo. of o r f Sin~fR~ Length ot noaent Length Index to the sptciren Average the forte of torque of the effective weight of a R 'Tt ga am work arn force aurtlr in ga 1; r# *t' ga Tropido lb notus Rattnake Cobra

55 tffective FORCE Of RETRACTION (UPPER JAN) BY THE H. PTERYGOIDEUS Snake No. of 'ft C o r ~ n Length of Moment Length lndtx to the ~peciaen Average the force of torque of the effective weight of a R 'TI ge nn work an forte nurcle in gr '12' an 'tt 9n w* Tropido notur Cobra TABLE XXl EfFfCTIVE FORCE OF RETRACTION (UPPER JAY) BY THE M. PTERVGOIDEUS ACCESSORIES Snake No. of Forte 'I' CorLn Length of Morent Length Index to the specimen Average the forte of torque of the effective weight of arr 'R'n 'Tt gn rr work a n forct austle in g1 '12'~... 'tt gn Tropido aotui

56 ti1ectlve IORCE 01 RETRACTION (UPPER JAW) BY THI I. RLTRIICTOR PTERYGOIDEI Snake No. of force 'F' CosLm Length of lerent Length Index to the spetinen lvcrage the forte of torque of the effectivr wright ~f arm 'Rfn 'TI gr ID wok a n force #uscle in gn 'L2fa~... 'tfgr Trcpido notus TABLE XXIV tiiec1iue FORCE 01 RETRACTION (UPPER JAW) BY THE I. RETRACTOR VOnlRIS Snake No, of force 'if CesLm Length of lorent Length Index to the specimen Average the force of torque of the effective weight of a R 'Tf ga aa work arm force nurcle in ga '12'" 't' $a ---_--_ Tropido notus Cobra

57 T1BLE XXV fffectivt forct Of RLTRICTION (UPPER J1Y) BY THE I. CERYICO-IANBIBULARIS Snake No. of Forte 'I' SinLfR: Length of lorent Length Index to the ~petiren bverage the forte of torque of the tffettive weight of ara 'htrr 'Tt ga am work rrr force rustle in gfi 'L:*am 'tt pn Tropido nstur Cobra * TALE XXVl fffcmiul forci Of RETRACTION (UPPER 1IW) BY THE I. IIURO-IIANDIBULARIS Snake No. cf force 'ft Cor~a Length of Nolent Length Index to the sgetiren Avtrage the fsrcr of torque of the effective weight ~t a n 'R2'1m 1 I 08 work a n forte #ustle in gr a 't' ga Tropido notus Ratsnake Cobra $ **

58 TABLE XXVIl IffECTIVf force 01 ABDUCTION PfR GRAB WEIGHT 01 I(USCLf lusrle Tropidonolus Ratsnrke Cobra... I. Orpressor mandibulae anterior I. Depressor aandibulae posttrior Total effective force of abduction in gram Total weight of nuscles involved in abduction ir~ gr-a~s fffertive forte of abduction in grams per gram weight of k b rustle

59 1FfICTIV1 FORC1 01 ADDUCTION PER GRlN YfIOHT OF BUSCLI... Bustle Tropidonotus Ratsnake Cobra I. Adduttor aandibular exttrnur ruptrficialis I. Adduttor aandibulat exttrnus atdialis I. Adductor mandibulac ewttrnus profundus I. Rdductor aandibulac posterior Pseudotenporalis Total effective forcr sf adduction in graar Total ncight of aurclrs involved in adduction in 3nw a * Effective forte of adduction in grans per gram weight of austlr

60 TABLE XXIX ffifctivf FORCE Of PROTRACTlON (UPPER JAW) PER ORAN HEIGHT Of HUSCLE... Uurcla Tropidonotur Ratsnake Cobra... I. Protractor pterygoidei I. Levator pttrygoidei U- Protractor quadrati ' * Total effective force of protraction in grass Total weight of rurclrr involved in protraction in gram * Effective force of protraction in gram per grat weight of ausrle...

61 IFfICTIVI rorce 01 PROTRACTION (LOUIR JAW) PIR GRAtl WEIGHT Of NUSCLE Nuscle Tropidonotus Ratsnake Cobra * * I. Pterygoidtus acrtrsories Total tfftctivt force of protraction in grars Total ~right of nuscles involved in protraction ' in gans... cfftctivc force of protraction in grans per gran weight sf auscle

62 TABLE XI11 EffECTIVE FORCE Of RETRACTlON (UPPER JAW) PER GRAH YEIOHT Of HUSCLE... luscle Tropidonotus Ratsnake Cobra I. Pterygoideus I.Pterygoideur acccsroricr #.Retractor pteryqoidei #.Retractor voaerir I.Ccrvico-randibularis I.Neuro-radibularis Total effective force of retraction in granr Total ~right of ruscles involved in retra6on in qrans Effective farcc of retrartian in grans per jrar weight of rustle

63 TABLE XXXlI INDICES TO THE EFfECTIYI FORCES OF THE FUNCTIONAL GROUPS OF HUSCLES PER GRdn WEIGHT Of MUSCLE Snake Abduction Adduction Protraction Protraction Retraction (upper jar) (lower jaw) (upper jar)... Cabra ,

64 From the various observations which have been noted here, pertaining to quantwve myolo~~y, the following details were seen: (1) The muscles associated with abduction were equipped with least potential effective forcegram weight of muscle in the three snakes. The potential effective force of protraction of lower jaw per gram weight of muscle was noted highest in tropidonotus and ratsnake, whereas in cobra the potential effective force of retraction of upper jaw was observed highest (Table - XXXII). (21 In the operations associated with adduction, protraction of upper and lower jaws and retraction of upper jaw, cobra was equipped with higher potential effective force per gram weight of muscle in comparison with that of tropidonotus and ratsnake. The potential effective force of abduction per gram weight of muscle was highest in ratsnake. In all the operations, tropidonotus showed least potential effective force per gram weight of muscle in comparison with that of ratsnake and cobra. (3) As far as the ratib of potential effective force per gram weight of muscle is concerned (Table - XXXII), the adduction was times and times, the protraction of upper jaw was times and times, the protraction of lower jaw was