THE SKULL. 



29 



decreasing- in width from before backwards. They are movably 



attached by their anterior broader ends to 



the tips of the projecting portions of the 



premaxillarv bones, and are so arranged 



as to bound the lateral margins of the 



nasal apertures, which they overlap. 



Nasal cartilages of frog, front 



view. 



a* Concha narinm. 

 PremaxiDarr bones, 

 r* .Ascending process of same. 

 m Upper j&w. 

 ' Lower jaw. 

 Olfactory capsule. 



Fig. 1 6 



6. The cartilaginous basis of the 

 skull, Primordial cranium (Figs. 14, 1 6). 



a. If the fronto-parietals be removed, 

 (Figs. 14, 1 6), a cartilage (*') is found 

 which partially closes the cranial cavity, 

 and which is usually perforated on either 

 side by a foramen (/'). 



More anteriorly in the 

 median line is found a 

 space (f) which ex- 

 tends to the spheneth- 

 raoid bone, and is only 

 closed by connective 

 tissue : posteriorly the 

 cartilage extends be- 

 tween the ex<x-cipitals 

 as far as the foramen 

 magnum, representing 

 Qx&osoccipUalenpt 



b. The 1-ase of the 

 cranium is (Fig. i6)also 

 partly cartilagin 



the parasphenoid (#) 

 be removed we find 

 above it a cartilage (*') 

 which passes back- 

 wards between the ex- 

 occipitals. and extends 

 as far back as the 

 foramen magnum : it 

 corresponds to the o* 

 occipitale la*ilare. 



c. The sides of the cranium are formed almost entirelv of car- 



Cartilaginons sknll of Rana ftevlevta, from below, twice 

 natural size. Cartilage shown bt stippling. 



