THE SKULL. 



29 



decreasing- in width from before backwards, 

 attached by their anterior broader ends to 

 the tips of the projecting" portions of the 

 joremaxillary bones, and are so arranged 

 as to bound the lateral margins of the 

 nasal apertures, which they overlap. 



They are movably 



Fk. i; 



X;v<al cai-tiliiges of frog, front 

 view. 

 (in Concha narinni. 

 i PreiiiaxiUary bones. 

 i' ^^scending process of same. 

 H» Upi^rjaw. 

 m' Lower jaw. 

 » Olfactory cai>*<ule. 



Fis. ,6./^ 



6. The cartilaginous basis of the 

 skull, Primordial cranium (Figs. 14, 16). 



a. If the fronto-parietals be removed, 

 (Figs. 14, 16), a cartilage (/) is found 

 which partially closes the cranial cavity, 

 and which is usually perforated on cither 

 side by a foramen (/'). 

 More anteriorly in the 

 median line is found a 

 space (/') which ex- 

 tends to the spheneth- 

 moid bone, and is only 

 closed by connective 

 tissue : posteriorly the 

 cartilage extends be- 

 tween the exoccipitals 

 as far as the foramen 

 viagnu 111, representi ng 

 theosoccijjiki/esttperi/us. 



b. The base of the 

 cranium is (Fig. 1 6) also 

 partly cartilaginous. If 

 the 2^ai'^^splienoid (s) 

 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 os 

 occipitale hasilare. 



e. The sides of the craniiim are formed almost entirelv of car- 



CartUaginou.s skvill of Uana esctilcnta, from below, twice 

 natural size. Cartilage shown by stippling. 



