ORDER OPHIDIA. 297 



In the heterodermatous serpents which are not venomous, 

 such as the boas and adders, all the bones of the upper jaw 

 are thus mobile on the cranium. 



The upper maxillary bones represent two long osseous 

 branches, in which the teeth are implanted. They form 

 the external edge of the foss of the palate. They are, like 

 a lever of the first order, articulated towards their middle 

 part, on a little bone analogous to the jugal, and which forms 

 the anterior edge of the orbit. Pretty nearly towards this 

 point, they have an apophysis which bears upon and glides 

 over the palatine arch. This double arthrosis, gives them 

 the faculty of performing a see-saw motion, and so much the 

 more so, as their anterior extremity is free, and the posterior 

 receives the extremity of a peculiar bone, which serves to 

 unite it to the palatine arches. 



These last are two osseous, interior branches, formed of 

 two parts. The one, anterior, is free in front, and articu- 

 lated behind, with an osseous stem, which proceeds towards 

 the articulation of the lower jaw, outwards, along with the 

 peculiar bone which unites it to the maxillary arch, and 

 above, over the base of the cranium, in front of the orbits. 

 The other, posterior , is analogous to the pterygoidian lamina, 

 and unites in front, with the posterior extremity of the first 

 portion behind, with the lower jaw on the internal side, and 

 outwards, with the bone which joins it to the maxillary arch. 



The incisive bones do not always carry teeth, and some- 

 times even, as is the case with the boas, they do not unite 

 the upper maxillary bones. 



Moreover, a final palato-maxillary bone, pretty nearly 

 cylindrical in its middle, and flatted at its extremities, is arti- 

 culated outwards with the posterior extremity of the maxil- 

 lary arch, and inwards with the middle and external part of 

 the pterygoidian region of the palatine arch. 



The heterodermatous serpents with venomous fangs, pre- 



