SKULL AMPHIBIA I 27 



lacrimal, may occur in front of the prefrontal. The parietal has a 

 descending postorbital process which {Necturus) may meet the 

 parasphenoid. The frontals extend from the parietals to the nasal 

 region. Posteriorly the squamosal (paraquadrate, 'tympanic') 

 extends from the parietal over the dorsal side of the otic capsule and 

 the quadrate, nearly to the hinge of the jaw. Many genera (Pletho- 

 dontidas, Amblystomidae) have a septomaxillary, traversed by the 

 lacrimal duct, developed in the membrane of the nasal capsule. The 

 tip of the cranium is formed by a pair of premaxillas (fused in Aniphi- 

 uma) which send processes back to meet the frontals. The rest of 

 the margin of the upper jaw is usually formed by the toothed maxillae, 

 but Perennibranchs lack maxillae. 



A large parasphenoid (developing late) occupies the middle of the 

 roof of the mouth and is toothed in many genera, and in so-called 

 Lechriodonts both vomers and palatines may bear teeth, the two bones 

 of a side frequently fusing to a vomero -palatine plate. The mem- 

 branous pterygoid (p. 126) also enters the oral roof and in some 

 genera meets the palatine. Those Lechriodonts with toothed para- 

 sphenoid lack a pterygoid bone. 



The only cartilage bone in the lower jaw is the articulare, except 

 in Proteus, said to have a mentomeckelian. Most of the jaw is 

 formed by membrane bones- — dentale, angulare, and sometimes a 

 splenial — the 'angulare' (possibly goniale, p. 121) may fuse with 

 the articulare. There are few ossifications in the hyo-branchial 

 skeleton. The most primitive are the Perennibranchs and the larvae 

 of other forms. Fusion of the dorsal ends of the arches of a side is 

 common. The number of arches persisting in the adult (fig. 132) 

 ranges from two (Salamandrina) to four (Perennibranchs and Dero- 

 tremes). The hyoid has cerato- and hypohyal parts. Hyoid and 

 first branchial arch are connected by a basihyal, scarcely distinct 

 from the middle part of the copula farther back. The other arches 

 are connected with the hyobranchial of the arch in front. Many 

 Salamandrina have an arcuate bar (fig. 132, E) in the floor of the 

 pharynx in front of the hyoid which connects the cornua of the two 

 sides. Another peculiarity is the separation in these same forms of 

 the posterior part of the copular apparatus as a distinct bone (os 

 thyreoideum or triquetrum, figure 132, £), lying just ventral to the 

 pharynx and in front of the pericardium. 



