44 THE FROG CHAP. 



and two small ( fori) spaces, called fontanelles, covered by 

 membrane. It has also a cartilaginous floor (Fig. 9, A) 

 underlaid by the paras phenoid. 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. qu), with which the 

 palatine and pterygoid bones are connected. Posteriorly 

 this bar is continuous with the cartilaginous groundwork 

 (quadrate) or core of the suspensorium (sus), which unites 

 above with the auditory capsule by two processes (Fig. g, 

 C, ot. pr, ped) and below furnishes an articular surface for 

 the lower jaw. 



Notice that in describing the vertebral column no dis- 

 tinction 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 suspen- 

 sorium, 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 Meckel'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 

 important offshoots. The anterior horns (Fig. 9, a.c.hy) 

 are long, delicate, cartilaginous rods which curve back- 

 wards and then upwards, finally joining with the audi- 

 tory capsules. The posterior horns (p.c.hy) are short, 



