8 4 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



process joining the otic capsule in front of the otic process. Cartilage bones are 

 few; supra- and basioccipital, alisphenoid and ethmoids are lacking; the otics fuse 

 to a single petrosal; an orbitosphenoid occurs and quadrate and pterygoid are 

 continuous. 



The roof of the adult skull is chiefly formed of parietals, frontals and nasals, 

 the latter being frequently separated by processes of the premaxillaries. Each 



FIG. 84. -Skull of Arriblystoma punclatum, after Wiedersheim. Letters as in fig. 68. 



frontal has a ventral process which limits the cranial cavity in front; there is usually 

 a prefrontal and a septomaxillary may be developed on the postero-lateral part of 

 the nasal capsule. A supratemporal is always lacking, the squamosal extending 

 up to the parietal. The upper jaw is composed of premaxillaries and (except some 

 perennibranchs, fig. 85) maxillaries; a jugal is always absent and the quadratojugal, 



FIG. 85. Skull of Proteus, after Wiedersheim. For letters see fig. 68. 



formed in the larva, fuses with the squamosal. In the roof of the mouth are the 

 large parasphenoid, frequently with teeth, and a pair of vomero-palatines, the 

 choanae lying behind the vomerine portion, which is farther back than in 

 the dipnoi. 



In the lower jaw Meckel's cartilage persists, its hinder end forming the articulare, 

 while in front it is surrounded by the dentary and splenial, each bearing teeth. In 

 the larvae the branchial skeleton is nearly typical, there being a hyoid and four gill 

 arches. In the adult, with the loss of aquatic respiration, the posterior arches are 



