SKULL. 267 



In the lower Urodela the notochord is constricted first \ertebrally, but 

 later owing to the great development of the iinossified intervertebral 

 connecting cartilage (Fig. 144, A and B, Jvh) it also becomes encroached 

 upon intervertebrally. This great development of intervertebral carti- 

 lage is the marked feature of the amphibian vertebra. In some forms 

 (Fig. 144 C) the intervertebral encroachment is very considerable, so 

 great indeed that in most Sa.lamandrines the notochord is entirely sup- 

 pressed and the intervertebral cartilage is segmented into a cup and ball 

 joint, one part uniting with the centrum of the anterior and the other 

 with that of the posterior vertebra (Fig. 144 D). The bony tissue of the 

 vertebral body would appear to make its appearance, in some cases ac 

 least, before the perichordal tissue has developed into cartilage. In the 

 centre of the vertebral bodies of certi^in forms some cai'tilaginous tissue 

 appears (Fig.ll44 A and C, GK), which is doubtless derived from the peri- 

 chordal cartilage, though it has been supposed by some anatomists to be 

 notochordal and therefore hypoblastic in origin.* In the Ani'.ra the 

 notochord persists in a few forjns vertebrally throughout life (Rami). 



The skull f of the Amphibia presents the following character- 

 istics. The cartilage is largely persistent, there being but few 

 cartilage bones ; the occipital region rarely has more than the 

 two exoccipitals which furnish the two occipital condyles ; 

 basioccipital, supraoccipital, basisphenoid, alisphenoid and 

 presphenoid bones are always or almost always absent ; there 

 is no interorbital septum ; well -developed paired frontal, parietal 

 and nasal membrane bones are found in the roof and an unpaired 

 parasphenoid and paired vomers in the floor ; the jaw suspension 

 is autostylic, the palato-quadrate bar being united at each end 

 with the skull ; the auditory region presents, for the first time, 

 a fenestra ovalis which is filled up by a cartilaginous plate, the 

 stapes (see p. 276). The quadrate, which in some cases remains 

 cartilaginous, is covered by a membrane bone, the squamosal 

 (paraquadrate). The visceral arches are in the larva five in 

 number (hyoid and four branchial). These become variously 

 reduced in the adult according to the condition of the breathing 

 organs, but the hyoid and traces at least of two branchials 

 generally persist together with a median ventral copula, of which 



* For a fuller account of the morphology of the vertebral colmim and 

 ribs of Amphibia see F. M. Balfour, Comparative Embryology vol. 2, London, 

 1885. H. Gadow. Phil. Trans. 1896, vol. 187, p. 1-57. E. Goppert 

 Morph. Jahrb., 22, 1S95. 



"I" In addition to the textbooks already cited (Reynolds, Marshall, 

 etc.) see Stohr, Z. f. iv. Z., 33 and 36 for the development of the 

 skull ; Gaup, Prinaordial craniurn etc. of Rana fusca, Morph. Arbeiten, 

 2 ; and W. K. Parker's varioxis memoirs in the Phil. Trans, of 1871 

 (Fros^. 1877 (Urodeles), 1881 (Batrachia) ; A. Davison op. cit. 



