my 



CLASS REPTILIA. 



nishing peculiarities, in our examination of the organs of 

 deglutition in the ophidians. 



In some homodermatous serpents, such as the acrochordus, 

 typhlops and amphisbsena, the two branches of the lower jaw are 

 soldered together, so that they cannot move either forward or 

 externally. They are short, and articulated to the condyle 

 by their most posterior point. These reptiles subsist only on 

 prey of a small size. 



But in all the heterodermatous serpents, the branches of 

 the lower jaw are simply united one to another by a liga- 

 mentous apparatus, which renders them mobile, and capable 

 of being approximated to, or removed from each other, at 

 the will of the animal, and the articulation of this jaw takes 

 place pretty nearly in the same manner as in birds ; for there 

 is no maxillary condyle, and at the posterior extremity of 

 the bone, is hollowed an articular facet, to receive an eminence 

 which has much analogy with the os qiiad^'atum, and from 

 which it diifers only by not being so mobile and so free. 



From this disposition it happens, that the lower jaw on 

 each side can not only be raised, and lowered, and open and 

 close the mouth, but also it can move outwards. Now, it 

 would have been difficulr that the branches of this lower jaw 

 should have been thus made capable of separation, without 

 permitting the upper at the same time to widen. This, in 

 fact, is what does take place in the majority of cases. The 

 upper jaw is as it were suspended, distinct from the cranium 

 and subordinate to the movements of the lower jaw, which by 

 the separation of its posterior extremities, obliges the ptery- 

 goidian arches to separate. This movement, by the approxi- 

 mation of their anterior extremities, simultaneously draws out- 

 wards the posterior extremities of the palatine and maxillary 

 arches, while if, on the contrary, the articular extremities of this 

 jaw tend to approximate, the anterior extremities of the same 

 arches proceed outwards, and are removed from each other. 



