154 ANIMAL BIOLOGY. [Part 1. 



distinctly composite. There is a central core of (Meckel's) car- 

 tilage which is ensheathed anteriorly by the dentary (d.). In 

 the hinder third of the jaw are three splints of bone, the angular 

 below (an.), the supra-angular (s. a.) and the splenial on the 

 inner side. And within the cartilage, at the hinder end, is a 

 further ossification, the articular (art.). All these tend to run 

 together in the mandible of the adult skull*in which posterior 

 and internal articular processes are well-marked. 



It is especially to be noted that the lower jaw does not articu- 

 late directly with the squamosal as in the rabbit, but is con- 

 nected with the brain-case by the intervention of a quadrate bone. 



(7.) TheHyoid. The hyo-branchial apparatus is composed of a 

 series of slender bones, the relations of which will be seen from 

 Fig. 49. The short anterior cornua (cerato-hyals) coalesce to 



FIG. 49. HYOID OF FOWL. 



a. c. Anterior cornu. b. h. Basi-hyal. gl. h. Glosso-hyal. p. c. Posterior 

 cornu. u. n. Uro-hyal. 



form a Y-shaped glosso-hyal. Lying behind this are two slender 

 median bones, one behind the other, the basi-hyal (b. h.) and the 

 uro-hyal (u. h.). From their point of junction spring the long 

 posterior cornua, in each of which there are two ossifications, a 

 proximal and a distal. 



(0.) The Frog's Skull. In the skull of even an adult frog 

 there is much more unossified cartilage than there is in the fowl 

 or the rabbit. There is, in fact, a chondrocranium or cartila- 

 ginous skull, which, partly invaded by bone, may be obtained by 

 maceration and stripping off the splints of bone which overlie it. 

 Fig. 50, A., shows a dorsal view of half this chondrocranium; 

 B. and C. are a ventral and dorsal aspect of the right side of 

 the bony skull ; E. shows the lower jaw, and D. the hyoid. 



