44 THE FROG chap. 



ginoiis floor (Fig. 9, A) underlaid by the parasphenoid. The olfactory 

 capsules (plf. cp) also have a cartilaginous roof and floor of irregular form, 

 with the posterior end of which is united the cartilaginous palato-quadrate 

 bar (pal. qu), with which the palatine and pterygoid bones are connected. 

 Posteriorly this bar is joined to the cartilaginous groundwork or core 

 of the suspensorium (sus), which unites above with the auditory capsule 

 by two processes (Fig. 9, C, ot.pr, ped) and below furnishes an articular 

 surface for the lower jaw. 



Notice that in describing the vertebral column no distinction was 

 drawn between cartilage- and membrane-bones. As a matter of fact the 

 vertebrae and the urostyle are all cartilage-bones ; each consists, in the 

 tadpole, of cartilage which subsequently undergoes ossification, i.e., 

 is replaced by bone in which a deposition of lime salts takes place. 



The lower jaw (Fig. 9, B) consists of two halves, or 

 rami, united with one another in front by Hgament. At 

 its posterior end each half bears on its upper surface a 

 shallow pit, by which it articulates with the suspensorium, 

 and a little in advance of this pit is an elevation of the 

 dorsal edge of the jaw, called the coronary process. 



Each half of the lower jaw consists of a cartilaginous core called Meckel's 

 cartilage, which furnishes the articular surface referred to, and in front is 

 ossified as a small cartilage-bone, the mento-meckeliaii (M.MCK). Out- 

 side the cartilage are two membrane-bones. One, the angulo-splenial, 

 extends along the inner surface and lower edge of the jaw and forms the 

 coronary process, while the dentary (DNT) forms the outer surface of 

 the anterior half of the jaw. 



The hyoid is a thin, shield shaped plate of cartilage 

 (Figs. 8 and 9, b. hy) produced, both in front and behind, 

 into a pair of processes or horns, as well as into less impor- 

 tant offshoots. The anterior horns (Fig. 9, a.c.hy) are long, 

 delicate, cartilaginous rods which curve backwards and then 

 upwards, finally uniting with the auditory capsules. The 

 pasterior horns {p.c.hy) are short bony rods which pass 

 backwards, diverging as they go, one on each side of the 

 glottis. 



