REPTILIA. 



283 



portion of the temporal fossa, until it meets the 

 jaw into which it is inserted, either separately 

 or conjointly with the anterior temporal. 



The posterior temporal (/), which is al- 

 ways distinct from the two others, descends 

 from the very posterior part of the temporal 

 fossa, along the zygomatic bone (tympanic') 

 (Jig. 205, 7), to the lower, into which it is 

 inserted behind the two others. 



The mouth is opened by means of a muscle 



Fig. 204. 



The Muscles of the Head of the Rattlesnake. 



a a, poison gland and its excretory duct ; e, 

 anterior temporal muscle ; f, posterior temporal 

 muscle ; g, digastricus ; h, external pterygoid 

 muscle ; i, middle temporal muscle ; q, articulo- 

 maxillary ligament which joins the aponeurotic 

 capsule of the poison gland ; r, the cervical angular 

 muscle; t, vertebro-mandibular muscle; u, costo- 

 mandibular muscle. (After Duvernoy.) 



analogous to the digastric (g), which arises 

 from the whole length of the posterior aspect 

 of the zygomatic (tympanic] bone, and ter- 

 minates on each side at the angle of the jaw 

 beyond its articulation. 



There is likewise a cutaneous muscle 

 which powerfully contributes to depress the 

 lower jaw, something like the platysma my- 

 oides ; this has been named the costo-mandibu- 

 laris (M). This, moreover, is assisted by a 

 strong fasciculus (t), derived from the spinous 

 processes of the vertebra immediately be- 

 hind the cranium, which has been distin- 

 guished by the name of the vertebro-mandi- 

 bularis. 



Two sets of muscles are appropriated to 

 the movement of the zygomatic (tympanic) 

 bone which supports the lower jaw : of 

 these one arises on each side from the back 

 of the occipital region, and is inserted into 

 the lower portion of the bone above referred 

 to. 



The other (fig. 205, w) is azygos, and has 

 been named by M. Duges sub-occipito articu- 

 laris, its fibres run across beneath the base 

 of the skull, from the articulation of the 

 lower jaw on the one side, to that on the 

 other. The former pair of muscles will draw 

 the branches of the lower jaw upwards and 

 inwards, the azygos muscle will move them 

 inwards and downwards. 



The anterior extremities of the lower jaw 

 can be approximated by a little muscle (fig. 



206, v), which passes transversely from one 

 to the other. This muscle, which is tendinous 



Fig. 205. 



Muscles of the Pterygo- Palatine Apparatus of the 

 Rattlesnake (Crotalus durissus). (After Du- 

 vernoy.} 



1, intermaxillary and nasal bones ; 2, 2, superior 

 maxillary bones; 3, external pterygoid bone; 4, 

 internal pterygoid bone ; 5, palatine arch ; 6, mas- 

 toid bone; 7, the tympanic bone; a, capsule of 

 the poison-gland ; a', duct of ditto; h, h, external 

 pterygoid muscle; k, internal pterygoid muscle; 

 /, /, spheno-pterygoid muscle ; TO, the suboccipito- 

 articular muscle (of Duges) ; n, the spheno-palatine 

 muscle ; o, the spheno-vomerine muscle. 



along the mesian line, is analogous to the 

 mylo-hyoideus; it likewise gives off a slip v', 

 which is attached to the skin. 



The muscles belonging to the maxillary 

 and palatine bones are, 



The external pterygoid (fig. 204, h), which, 

 arising from each jaw, runs directly forward 

 as far as the maxillary extremity of the exter- 

 nal pterygoid bone, which it draws powerfully 

 backwards. In venomous serpents with an- 

 terior poison fangs, which have the external 

 pterygoids very long, and the maxillary bones 

 very short, this muscle is very strong, arising 

 by aponeurotic fibres, from the capsule which 

 encloses the articulation of the lower jaw, 

 whence it runs forwards towards the pouch 

 in which the venomous teeth are lodged, upon 

 which it is partially spread out ; its principal 

 attachment, however, is to the posterior apo- 

 physis of the superior-maxillary bone, into 

 which it is inserted by a distinct tendon. The 

 use of this muscle is evidently to carry back- 

 wards the venomous fangs when they are to be 

 laid flat, and to incline them towards the pa- 

 late, a position that they retain while in a state 



