l.p.f. 



au. P^o. 



0. c. .ex. 



— The cartilaginous skull of a 

 seen from above after the 

 removal of most of the bones. 



Fig. 267 



frog. 



/• 



a.f.. Anterior fontanelle ; au., auditory capsule ; cr., 

 cranium ; ex., exoccipital ; l.p.f., left posterior 

 fontanelle ; nas., nasal capsule ; o.c, occipital 

 condyle ; pro., pro-otic ; pt. pterygoid ; q., quad- 

 rate ; q.j., quadratojugal ; sp., sphenethmoid; 

 u.j., upper jaw bar. 



SKULL 353 



The wall of the cranium has a number of openings or foramina, 



for the passage of the nerves 



and arteries. The first cranial 



nerve of each side passes through 



a foramen in the transverse 



partition of the sphenethmoid 



on its way from the organ of 



smell in the nasal capsule. The 



second nerve, which serves the 



eye, enters the skull through a 



conspicuous opening on each 



side in the middle of the sphenoi- 

 dal region. The third and fourth 



nerves have each a minute 



foramen in the side of the same 



region. The fifth and seventh 



nerves pass through a large com- 

 mon opening on the under side 



of the skull, situated in a notch 



in the pro-otic bone mentioned 



below. The foramen for the sixth nerve is a small opening between 



those for the second and for the fifth and seventh. The eighth 



nerve enters from the inner 

 part of the ear by an opening 

 in the wall between the cranium 

 and the auditory capsule. A 

 foramen for the ninth and 

 tenth nerves is situated in the 

 exoccipital bone, at the side 

 of the occipital cond3de. 



The auditory capsules are 

 blocks of cartilage continuous 

 with that of the cranium, and 

 applied to its posterior corners. 

 Each contains a complicated 

 space, the cartilaginous laby- 

 rinth, which lodges a structure 

 known as ' the membranous 

 labyrinth of the ear'. Part of 

 the front of the capsule is 

 ossified to form the pro-otic 



Fig. 268. — Skull of frog, ventral. — From 

 Young, The Life of Vertebrates, 1050. 

 Clarendon Press, Oxford. After 

 Marshall. 



col., Columella auris ; ex., exoccipital ; f.p. , fronto- 

 parietal ; m., maxilla ; n., nostril ; pa., palatine ; 

 par., parasphenoid ; pm., premaxilla ; pro., pro- 

 otic ; pt., pterygoid ; q., quadrate ; qj., quadrato- 

 jugal ; se., sphenethmoid ; sq., squamosal ; 

 v., vomer. 



