92 COMPARATIVE MORPHOLOGY OF VERTEBRATES 



and quadratojugal being absent, while a large prefrontal and a larger postfrontal 

 (usually called squamosal) occur. In the roof of the mouth maxillary and 

 palatine are fused, the vomers distinct, while the united parasphenoid and basi- 

 occipital form a large os basale. In the lower jaw there are only dentary and 

 angulare, the latter being produced behind the articulare in a remarkable way. 



In the cartilage skull of the Urodeles (fig. 91) the pterygoid does not usu- 

 ally reach the anterior part of the skull but projects as a process from the quad- 

 rate, which bears, besides the two processes already mentioned fp. 89), a 

 palatobasal process joining the otic capsule in front of the otic process. Carti- 

 lage 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 

 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 squa- 

 mosal extending up to the parietal. The upper jaw is composed of premaxillaries 

 and (except some perennibranchs, fig. 94) maxillaries; a jugal is always absent 



_ Fig. 94. — Skull of Proteus, after Wiedersheim. bh, basibranchial; cb, ceratobran- 

 chial; ch, ceratohyal; d, dentary; eb, epibranchial ; eo, exoccipital; /, frontal; p, parietal; 

 pm, premaxillary; q, quadrate; sq, squamosal; st, stapes; v, vomer; cartilages dotted. 



and the quadratojugal, 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 choanal lying behind the vomerine portion, which 

 is farther back than in the dipnoi (fig. 93). 



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 reduced or even disappear, those remaining being 

 connected by a one- or two-jointed copula. 



The chondrocranium of the larval Anura {Rana, fig. 95) differs consider- 

 ably from that of other amphibia as well as from the adult conditions. Like all 

 amphibians it is platybasic. The pterygoquadrate has, besides the normal otic 

 and epipterygoid processes, a cranio-quadrate process connected with the nasal 

 region, in front of which is the articulation of the lower jaw. In front of the 

 cornua are a pair of suprarostral cartilages and a similar pair of infrarostrals lie 

 in front of the Meckelian, from which they are apparently derived. These 



