530 URODELA [CH. 



In the skull the cranium is cylindrical, being quite uncom- 

 pressed between the eyes. The bones of the jaws and face are 

 widely arched outwards, so that the whole skull has a flattened 

 shape. The nasal and auditory capsules form easily recognisable 

 buttresses projecting from the cranium. 



In both the floor and roof of the cartilaginous cranium the 

 proper wall is largely deficient. The deficiency of the roof is the 

 anterior fontanelle, that of the floor the greatly enlarged pituitary 

 fossa. But these deficiencies are not seen in the uninjured skull, 

 because the hole in the roof is closed in by two pairs of dermal 

 bones, the frontals and the parietals, and that in the floor is 

 underlaid by a broad parasphenoid dermal bone (Fig. 255). 



Only at its extreme front and hind ends is the wall of the cranium 

 converted into cartilage bone. In front there is on each side an 

 orbi to sphenoid bone, in the side wall, extending into the roof 

 and floor and ossifying also the hinder wall of the nasal sac ; behind, 

 two exoccipital bones are placed at the sides of the foramen 

 magnum, which they nearly encircle (Fig. 255). These bones bear 

 the two condyles, so characteristic of Amphibia, for articulation 

 with the vertebral column. There is no basi-occipital ossification, 

 and in this point again Amphibia resemble Dipnoi. 



The first visceral arch, which constitutes the cartilaginous jaws, is 

 almost entirely cartilaginous. It consists of an upper part immov- 

 ably attached to the skull, corresponding to the pterygoquadrate 

 bar or upper jaw of Fish, and a lower part, Meckel's cartilage, 

 forming the basis of the lower jaw. It will thus be seen that 

 Amphibia resemble Holocephali and Dipnoi in this point. If we 

 call this condition autostylic we do not do justice to the full extent 

 of the resemblance between Dipnoi and Amphibia, for the jaw in 

 the Notidanidae, which is movably articulated with the cranium, 

 is also said to be autostylic. The name holostylic has been 

 proposed for the condition of immovable junction between the 

 cartilaginous upper jaw and the cranium, and this name we shall 

 adopt. The same is true of all the higher groups of the Craniata. 

 The upper jaw consists of two regions, the suspensorium which 

 is fused with the skull and to which the lower jaw is attached, and 

 the pterygoid process, a spur of cartilage which runs forward 

 towards the nasal capsule. Both suspensorium and the articular 

 end of Meckel's cartilage are slightly calcified. They are de- 

 nominated quadrate and articular in Fig. 255, but there is no 

 true bone present in either case. The front of the auditory capsule 



