OF THE SKULL IN THE AMPHIBIA URODELA. 173 



that, agree with this of the highest kind of " Caducibranchiate " Urodele. I shall 

 therefore carefully set down the characteristics of this skull, and then it can be used as a 

 measure, being " perfectissimum in suo genere," of the lowness or height, in type, of the 

 skulls of other Urodeles, and also as a test of Avhat is normal or aberrant in the skulls of 

 the Batrachia. This sj)ecies and Ran a temporaria, therefore, will be taken as con- 

 venient, and yet worthy, representative Salamandrian and Batrachian types. They are 

 culminatiug forms, being most perfectly specialized according to then- kind. The 

 general resemblance of this skull to that of a Grey Frog is seen at once (PI. XVI. 

 figs. 1-3) ; but attention to details will give us a large number of important differences. 



When this skull is stripped of its investing bones (fig. 1) we see how little change, 

 except that of ossification and increase of size, has taken place. The very strong occipital 

 arch has this normal amphibian weakness, namely, that an oblong tract both of roof 

 and floor remains unossified ; in the floor the shrunken notochord still remains. 



The condyles (oc.c) are best seen from below (fig. 2) ; they arc large, oval, and slightly 

 pedunculated ; they are very wide apart. A large rounded fossa divides this arch above, 

 on each side, from the periotic mass, but there is no suture ; below, the regions melt 

 insensibly into one another (fig. 2). But both below and on the inside (fig. 5) the double 

 passage for the glossopharyngeal and vagus marks the bounds of these two territories. 

 The occipital ring expands greatly on each side to embrace and unite with the large ear- 

 masses ; but both above and below the shortness of the cartilaginous tracts causes an 

 emarginatiou of great size, both before and behind, in this annular growth. 



The front emarginatiou of the floor is the hinder margin of the posterior basicranial 

 fontanelle; its fore boundary is formed by a bridge (a.tr.), which is cartilaginous 

 in the middle and bony at its large piers. Did these osseous tracts meet, we should have 

 the " prootic bridge" of the Bony Pishes; the real morphological nature of this band 

 is of great interest. 



The hinder part or threshold of the skull was formed by the separate and somewhat 

 late " parachordals," or investing mass ; the bridge is formed by the posterior ends of 

 the trabecular, which had united, in the first stage described, with the parachordals, and 

 ran into each other in front of the notochord (PI. XIV. fig. 1, nc, tr, iv). So that two 

 things have taken place — much of the cartilage has become bone, and old cracks have 

 opened again, by relative shrinking of that which does not ossify. 



The occipital arch is not more strongly united to the auditory masses than the 

 trabecular walls ; the alisphenoidal region is strongly cemented to these masses by a 

 remarkable trespass of each prootic centre. 



The early condition of the trabecula alone can explain this curious encloskeletal skull. 

 These rods embrace the notochord by their hinder ends, and then turn rather suddenly 

 outwards (Huxley on Menobranchus, P. Z. S. 1874, pi. xxxi. figs. 1, 2, Tr, Gh). 



In this adult skull the confluent ends of the trabecular form a thin narrow band of 

 cartilage, passing transversely (with a little backward deflection) across the cranial 

 floor. Towards the side each bar suddenly thickens, and is bent on itself so as to form 

 an acute angle ; in front of the bend it becomes very solid, and at the bend there is the 



SECOND SERIES. — ZOOLOGY, VOL. II. 24 



