298 CLASS REPTILIA. 



sent a new modification, because in them, not only can the 

 jaws separate, but also because their upper maxillary bones 

 are capable of being moved forwards. The palatine arches 

 are very short, entirely directed forward, and carry none but 

 venomous teeth. An intermediate bone proceeding above the 

 upper maxillary, which is itself articulated in front of the 

 orbit, over the short and mobile cheek-bone, imites them to 

 the pterygoidian arches, so that by the movement of the 

 lower jaw in front, the palatine arch, drawn in this direction, 

 drives before it the bone which unites it to the maxillary, 

 which last, being extremely mobile, rises immediately, and 

 proceeds forward, being put in play over the bone of the cheek. 



It is clearly to the conformation we have now described, 

 that the majority of the ophidians are indebted for the singu- 

 lar faculty which they possess of dilating their throat so as 

 to swallow bodies larger than themselves, as we have already 

 mentioned. 



The muscles which produce this dilatation deserve to ,be 

 known, and present numerous peculiarities. 



All those of the lower jaw are concealed in the thickness 

 of the lips, and form, on each side, the circumference of 

 the mouth. One of them, which appears to be the substitute 

 of the masseter, is stronger, and constituting the anterior edge 

 of the commissure of the lips, proceeds, through a great ex- 

 tent, to terminate, at the upper edge of the submaxillary 

 branch, after having taken its origin by a strong aponeurosis 

 on the tendinous purse, which encloses the poison bladder. 

 We find immediately behind it the analogue of the tem- 

 poral muscle, which is only a small fleshy band, which 

 is confounded below with the preceding, and descends 

 by an emargination behind the orbit. Still farther back, 

 over all the lower part of the os quadratum, there is a 

 peculiar muscle, which is an accessory of the temporal and 

 the masseter, while the analogue of the digastric occupies the 



