72 THE OSTEOLOGY OF THE REPTILES 



joint between the angular and splenial; a similar joint, though less 

 well developed, is found in the monitor lizards. The mandibles are 

 usually united in front by suture but are ligamentously connected in 

 the mosasaurs and some land lizards. 



As is seen, there are many variations in the skull of the lizards, 

 more than in many other groups of reptiles called orders. 



Ophidia or Serpentes 



(Figs. 59 a-e) 



The skull of snakes differs from that of lizards, especially in the 

 complete closure of the brain cavity in front by descending plates 

 from the parietals and frontals, the former always meeting the 

 basisphenoid below, the latter sometimes interrupted by the coa- 

 lesced optic foramina; in the constant absence of the postoptics, 

 epiptery golds, and squamosals, the quadrate articulates proximally 

 with the tabular only, which may also be absent. The parietals are 

 always fused; there is no parietal foramen. There is no temporal 

 arch, and, rarely, no ectopterygoid. The premaxillae are small and 

 often edentulous, the maxillae rarely edentulous. The pterygoids 

 and palatines usually bear long teeth. The postorbitals may meet 

 the maxillae below, and there is no jugal. 



The vipers (Fig. 59 e) have but one functional tooth attached to 

 the maxilla. It is hollow, with an opening at its base and another 

 near its apex for the passage of venom. Only the dentary is freely 

 articulated in the mandible, the posterior bones closely fused; the 

 two mandibles are usually united in front by ligament only. There 

 is no ossified interorbital septum, and the prootics are largely ex- 

 posed on the side of the skull. 



The mandible of Ophidia has the primitive structure, except that 

 the coronoid appears to be absent or fused, the bone usually so 

 called being clearly the prearticular. The long splenial, as usual in 

 reptiles with a long median symphysis of the mandibles, enters into 

 the symphysis. 



The conical teeth of the premaxillae, maxillae, and dentaries 

 primitively were inserted in sockets, but in the more specialized 

 types are rather loosely lodged in grooves. 



