44 THE FROG CHAP. 



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

 capsules (olf. 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. qti], with which the palatine and pterygoid bones are connected. 

 Posteriorly this bar is continuous with the cartilaginous (quadrate] 

 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 replacing and investing bones. As a matter of fact the vertebrae 

 and the urostyle are all replacing 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 ligament. 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, the 

 mandibular or MeckeF s cartilage^ which furnishes the articular surface 

 referred to, and in front is ossified as a small replacing bone, the mento- 

 meckelian (M. MCK). Outside the cartilage are two investing 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 joining with the auditory capsules. The 

 posterior horns (ti.c.hy) are short bony rods which pass 

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

 glottis. 



