284- 



REPTILIA. 



of repose, in which condition it covers them 

 by drawing the inclosing pouch over them. 



The internal pterygoid (/c), shorter and 

 smaller than the external, runs from the alar 

 bone to the posterior part of the lower jaw, 

 which it consequently draws forwards. 



The spheno-pterygoid (I), which has no ana- 

 logue in other vertebrata, arises from the 

 mesial portion of the base of the cranium, 

 and runs outwards and backwards to be at- 

 tached to the inner surface of the pterygoid 

 plate, which it can thus drag forwards and 

 inwards so as to cause the protraction of the 

 superior maxillary bone, thus raising the 

 venom fangs ; it will likewise narrow the 

 mouth by causing the approximation of the 

 two internal arches. It is assisted in its ac- 

 tion by a muscle, which Cuvier regards as a 

 dismemberment of the temporal, the post-or- 

 bito-palat'me, which runs from the temporal 

 fossa behind the orbit to the palatine arch. 



The spheno-palatine (fig. 205, n) antagonises 

 the two last ; it extends from all the length of 

 the palatine arch to the mesial line of the 

 base of the cranium ; its direction crossing 

 that of the preceding muscle, above which it 

 is placed. By its contraction it brings back- 

 wards the entire upper jaw, approximating at 

 the same time the branches that form it. 



Two small muscles (Jig. 205, o) advance 

 from beneath the sphenoid, and run close to 

 each other to be inserted by a slender tendon 

 into the vomer. These are the spheno-vomerine 

 muscles of Duges, for which it would be dif- 

 ficult to find analogues. These muscles de- 

 press the muzzle. 



In all the true serpents the tongue is en- 

 closed in a membranous sheath, to be de- 

 scribed hereafter ; and the os hyoides, which 

 in the ophidia has no connexion with the 

 larynx, consists of two simple cartilaginous 

 stems (fig. 206, B,) running parallel to each 

 other, which bend forwards underneath the 

 sheath of the tongue, where they unite to form 

 a sort of arch of almost membranous consis- 

 tency. Corresponding with this simple form 

 of the os hyoides; the hyoid system of 

 muscles is very simple. The mylo-hyoideus, 

 above described as being an adductorof thetwo 

 divisions of the lower jaw, has some of its 

 fibres confounded with those of the costo- 

 mandibular muscles (figs. 204. 206, u}, which, 

 coming from the anterior ribs, is attached to 

 the lower margin of the inferior maxilla. Its 

 central fasciculi are adherent to the rami of 

 the os hyoides, and more especially to the 

 membranous arch which they form in front. 

 They can therefore draw it either forwards or 

 backwards, accordingly as it is the maxillary 

 or the costal portion which contracts; and 

 thus these fasciculi hold the place of both 

 sterno-hyoidei and genio-hyoidei. In ser- 

 pents, therefore, there are no muscles exclu- 

 sively appropriated to the os hyoides. 



The tongue of serpents is slender, cylindri- 

 cal, and forked at its extremity. It is lodged 

 in a membranous sheath, the opening of which 

 is situated near the anterior part of the mouth, 

 and the animal can protrude it from its mouth 



to nearly its whole length, using it as an in- 

 strument of touch, apparently comparable in 



Fig. 200. 



Muscles of the Throat of the Rattlesnake (Crotalus 

 durissus'). 



A, retractor muscles of the tongue (Hyo-vagi- 

 niens) ; B, cornua of the os-Hyoides ; A, external 

 pterygoid ; u, u, u, u, costo-mandibular muscles ; 

 v, ,"anterior adductor muscle of the rami of the 

 lower jaw ; v, v f , portion of the preceding connected 

 with the skin of the throat ; x, posterior adductor 

 of the rami of the lower jaw ; y, a muscle running 

 from the symphysis of the lower jaw to the sides of 

 the trachea (genio-trachien) ; z, geno-vaginalis, 

 representing the genio-glossi ; z!, z", external and 

 internal origins of ditto. 



some respects to the antennae of insects. 

 The muscles by the agency of which it is pro- 

 truded, are the genio-vaginales (fig. 206, ), re- 

 presenting the genio-glossi. These arise by 

 two fasciculi, of which the internal and small- 

 est (z') arises from the tendinous median 

 portion of the adductor of the inferior 

 maxillae (i>); whilst the external (2"), which is 

 the strongest, takes its origin from the ex- 

 tremity of the lower jaw itself : these two 

 portions unite and form a narrow band, which 

 becomes applied to the sides of the sheath of 

 the tongue, along which it is continued back- 

 wards to its extremity. 



The retractors of the tongue (fig. 206, A) are 

 analogous to the hyo-glossi ; they arise around 

 the extremities of the rami of the os hyoides, 

 and running forwards conjointly, enter the 

 sheath of the tongue, and its proper investing 

 membrane ; so that they constitute the entire 



