OF THE SKULL IN THE AMPHIBIA UEODELA. 199 



The under face of this ear-capsule is very different from that of most high " Uro- 

 delous " skulls. 



In those massive typical Caducibranch skulls just described, e. g. Notophtlialmus 

 (PI. XVII.) and Cynops (PL XVIII. ), the vestibule is in the form of a smooth bulla, 

 with the stapes set on behind ; and that plate is either quite soft or very slightly ossified ; 

 it is also relatively small. 



In Spelerpes (PI. XXI. figs. 2, 3, and PL XVIII. fig. 10) the vestibule is but little pro- 

 tuberant ; its fenestra is lateral, and, corresponding with the stapes, very large. 



At the inner margin of the fenestra the bone is scooped, and partly unossified at the 

 edge. This is seen in the oblique view (PL XVIII. fig. 10). The outer margin of the 

 fenestra ovaiis is right under the tegmen, made larger and more beetling by the postero- 

 inferior edge of the squamosal (sq). This change of position is due to a sort of vegeta- 

 tive affinity or attraction between the stapes and the stapedial rod (st, co), which is found 

 in the inner layer of the temporal plane. 



The 7th nerve (7) first burrows in and then grooves the prootic a good distance in 

 front of the stapes ; in its escape it curves a little backwards, and then turns obliquely 

 forwards and outwards under the otic process and its ossifying quadrate centre. 



It will at once be seen that this is a very different relation of nerve and rod to what 

 is seen in the Batrachia, where the hyomandibular, mostly late in appearance, passes 

 under the facial nerve to apply itself, not to the outer face of the stapes, but along its 

 antero-superior margin, pushing into the scooped fossa that leads to the fenestra ovaiis. 

 Moreover, in the Batrachia the stapes never yields any bony matter to the columella ; 

 in them the stapes is seldom ossified ; and the columella generally cuts off the segment 

 that grows into the front of the fenestral fossa. 



One more point of interest is to be noted here : the lowest Perennibranchs have their 

 stapes thoroughly ossified ; the highest Caducibranchs, like the Batrachia, have it soft ; 

 here, in Spelerpes, it ossifies early, and becomes a very perfect and elegant shutter 

 to that small oval window. 



In the walls of the skull, from the foramen ovale (PL XXI. figs. 3, 5) to a small opening 

 behind the optic passage (2), the alisphenoidal region is soft ; then the wall is hard, up 

 to a small distance from the nasal sacs. 



The nasal sacs (fig. 1, na) can be seen outside their roof-bones and also in front, forming 

 a rim to the external nostrils (e.n) ; but on the whole they are most carefully encased 

 in bone. 



Yet in the last stage these olfactory paraneurals were not chondrified, nor even the 

 nasals, ectethmoidals, or maxillaries developed. 



The condyle of the suspensorium reaches further forwards than the foramen ovale (5); 

 it is scooped in an angular manner (fig. 2), and above it the quadrate (q) grows upwards 

 to the pterygoid cartilage in front, and to the top of the otic process behind. But the 

 pterygoid cartilage and its base, running upwards as the ascending process to the alisphe- 

 noidal wall, is all soft. 



In this thing Spelerpes is contrary to the ordinary Caducibranchs, namely, that 



27* 



