208 



THE FROG. 



QP), which becomes drawn out to form the framework of the 

 upper jaw. At the same time, Meckel's cartilage, MC, forming 

 the basis of the lower jaw, becomes also greatly lengthened, 

 while the lower labial cartilages disappear. At the time of the 

 metamorphosis, the quadrate still slopes downwards and forwards 

 (Fig. 93) ; but the rotation continues until the quadrate becomes 

 vertical, and finally, before the end of the first year, acquires 

 the inclination downwards and backwards so characteristic of 



EC CL QE 



BR.4- EB BR.2 HR Q MC 



FlG. 93. Skull of a Tailed Frog towards the close of the metamorphosis, from 

 the right side. The head and eye are represented in outline, x 13. 



BB, basibraiichial. BR.2, BR.4, second and fourth branchial bars. CL, cohiniclla. 

 EC, auditory capsule. HR, ceratnhyal. MC, Meckel's cartilage. OC, outline of eye. 

 OF, olfactory capsule. OL, outline of lens. ON, foramen for optic nerve. Q, 

 quadrate. Q,E. connection of quadrate with auditory capsule. Q,O, orbital process of 

 quadrate. QP, palato-pterygoid process. SA, stapes. 



the adult (Fig. 94). The orbital process of the quadrate early 

 becomes inconspicuous (Fig. 93, QO), and finally disappears. 



The hyoid bar, which is massive in the tadpole, becomes very 

 slender in the frog. It gradually elongates, extending dorsal- 

 wards until it meets, and fuses with, the ventral surface of the 

 auditory capsule (Fig. 94, H). 



The branchial bars become more and more slender as the 

 gills begin to shrink, and ultimately disappear almost completely. 

 The basihyal and basibranchial cartilages give rise to the body 

 of the hyoid (Fig. 94, H) : from the ventral ends of the fourth 



