30 



MANUAL OF ELEMENTARY ZOOLOGY 



front, and the ninth projects in front, to articulate with the 

 hollow of the eighth, and has behind two knobs which 

 articulate with two hollows on the urostyle. The latter is a 

 long, tapering bone with a ridge above, in the front part of 

 which is a canal for the hinder part of the spinal cord. 



In the skull, the following regions may be distinguished : 



sku|| (i) the cranium or brain case, (2) the nasal 



capsules, which enclose the organs of smell, (3) 



the auditory capsules, which enclose the inner part of the 



ear, (4) the 



p.m. 



'"II. 



col. pro. ex. o.c. IX.X. V.VII. 

 Fig. 12. — The skull of a frog, seen from below. 



col. j Columella; ex., exoccipital ; *'.«., internal narial open- 

 ing ; m., maxilla; o.c, occipital condyle; pi., palatine; 

 p.m., premaxilla ; pro., prootic ; prs., parasphenoid ; 

 pt., pterygoid ; t/.J., quadratojngal ; sp., sphenethmoid ; 

 v., vomer ; v.t., vomerine teeth; If, V, VI, VII, IX, 

 X, foramina for cranial nerves. 



visceral arches, 

 an apparatus 

 which lies 

 below the 

 cranium and 

 is highly de- 

 veloped in a 

 fish and in the 

 tadpole, but in 

 the adult frog 

 is represented 

 only by the 

 jaws and by 

 a structure in 

 the floor of 

 the mouth 

 known as the 

 hyoid. 



The cranium 

 is an oblong 

 box, from 

 which the 



nasal capsules 

 project in front and the auditory capsules at the sides 

 of the hinder end, while the bones of the upper jaw 

 form a scaffolding fixed to the capsules and supporting 

 the sides of the head. Between the scaffolding and the 

 cranium is on each side a large space known as the orbit 

 in which lies the eye. The hinder part of the cranium, 

 between the auditory capsules, is known as the occipital 

 region, the middle part, between the orbits, is known as 



