THE SKULL 85 



parasphenoid. These relations are secondary, for in the larval 

 condition a typical palatoquadrate or pterygopalatine bar is present 

 (Fig. 63). The lamina cribrosa (p. 74) is either cartilaginous {e.g., 

 Salamandra) or membranous (e.g., Triton) ; or the cranial cavity 

 may be closed in front by special modifications of the frontals. 



On the outer side of the vomer lies the maxilla, and in front of 

 this is a premaxilla which usually encloses, or at least bounds, a 

 cavity. The latter bone extends on to the dorsal surface of the 

 skull and abuts against the nasai, behind which usually follows a 

 prefrontal. 



The suspensorium is much more simple than that of Fishes 

 (Figs. 63 — 66). It consists of the quadrate only, which has 

 usually four typical processes connecting it with surrounding parts, 

 and which becomes fused secondarily with the skull. On the 

 outer surface of the quadrate an investing bone, the squamosal,^ 

 becomes developed. 



Ill Tylototritoii verrucosus the quadrate sends forwards a process -which 

 connects it with the maxilla : this is quite exceptional amongst Urodeles. 



With the exception of the lower jaw, in connection with which 

 articular, splenial, and dentary bones are developed, the visceral 

 skeleton of Urodeles undergoes various modifications in the different 

 types. We may consider the ground-form, as exhibited in the larva, 

 to consist of five pairs of bars in addition to the mandibular arch 

 (Fig. 66). The anterior bar, or hyoid, consists of two segments (Fig. 

 67, A), as do also the two first branchial arches. The third and 

 fourth branchial arches are much smaller, and each is composed of 

 a single segment. All the above-named arches are connected 

 with their fellows of the other side by means of a single or double 

 basal piece. At the close of larval life, that is, when the gills are 

 lost, the two hinder pairs of arches disappear entirely, while the 

 two anterior pairs undergo chauges as regards form and position, 

 and may become more or less densely ossified (Fig. 67, B — D). 



In the genus Spelerpes, which possesses a sling-like tongue, the dorsal 

 segment of the first branchial arch grows out mto a long cartilaginous fila- 

 ment, which extends far back under the dorsal integument (Fig. 67, D). 



The skull of the Gymnophiona differs from that of Urodeles mainly in its 

 extremely solid and strong character, the ossifications being more extensive. 



In the extinct tailed Amphibians (i.e., Stegocephala, Fig. 68) some of which 

 were comparatively gigantic, the cranial bones were very numerous and dense. 

 A parietctl foramen was present, as well as a ring of orbital bones. These 

 forms possessed the same number of visceral arches as Urodeles, and it has 

 been shown that they (e.g., Branchiosaurus) underwent a metamorphosis. 

 Existing Amphibia cannot have been derived directly from them. 



Anura. — The skull of the tailless Batrachia is at first sight 

 very similar to that of Urodeles. It undergoes, however, an 



' According to Gaupp, a true squamosal is never present in existing Amphibia, 

 and the bone wliich is usually so designated he call.s the 2Mraquadratc 



