202 



THE FROG. 



only a slight tendency to develop processes, and by being 

 almost completely devoid of yolk-granules. 



FIG. 90 



tM n 



^ RL PM 



BS 



.QO 



RL 



CH BP.4- BR3BR.2 BK.i 



FIG. 91. 



FIG. 92. 



FIG. 90. The skull of a 12 mm. Tadpole, seen from the right side. The 

 notochord, the brain, and the entire head are represented in outline, in 

 order to show the relations of the skull to them, x 30. 



FIG. 91. The same skull from the dorsal surface. The lower jaw, and the 

 hyoidean and branchial bars are omitted, x 30. 



FIG. 92. -The same skull from the ventral surface, x 30. 



BB, basi-branehial. BH, roof of hiinl-brain. BM, roof of mid-brain. BR.l. 

 BR.2, BR.3. BR.4, first, second, third, and fourth branchial bars. BS, cerebnil 

 hemisphere. CH, notochord. EC, auditory capsule. HB, basihyal. HO, urohynl. 

 HQ,, articulation of ceratohyal with quadrate. HR, ceratohyal. JL, lower jaw. JTJ, 

 upper jaw. LI, upper lip. LJ, lower lip. LL, lower labial cartilage. LTJ, upper 

 labial cartilage. MC, Jleckel's cartilage. PW, pineal bodv. Q, quadrate. QO, 

 orbital processof quadrate. QP, palato-pterygoid process. Q,R, connection of quadrate 

 witli trabecula. RC, pai-achonlal cartilage. RL, trabccula cranii. SA, meuibranous 

 patch in the outer wall of the auditory capsule, in which the stapes is developed at a 

 slightly later stage. X. clioroid plexus of third ventricle. 



In the next stage the cells become still more closely com- 



