THE BRAIN. 



119 



third ventric le ; from it the pineal bod y and the i nfandibnlnm 

 are developed as median diverticula, dg rsal and ventral re spec- 

 tively ; while the o ptic vesicles and c erebral hemi spheres arise 

 as paired lateral and anterior outgrowt hs. 



The mid-brain undergoes comparatively little change ; from 

 its roof the optic lobes of the adult are formed. 



The hi nd-brain becomes the medulla oblongata of the ad ult : 

 from the roof of its anterior part the cerebellum is formed . 



Before considering the development of the several parts of 

 the brain in detail it will be well to notice the general proper- 



Fig. 62. 



Fig. (13. 



Fig. 62.— The brain of the adult Frog : dorsal surface. 

 Fig. 63.— The brain of the adult Frog : ventral surface. 



x4. 

 x4. 



C cerebeHum. CH, cerebral hemisphere. CP, choroiii plexus ol third ventnclo. 

 p fourth veatricle. IIT, inflindibulufc. M, niecUiUa oblongata. O, ollactory lobe. 

 OC optic chiasma. OL, op'tib lobe. P, stalk of pineal body. PJ, pituitary body. 

 T thalameiicephalon. I, olfactory nerTe. II, qptto-aerve. Hirtlurd or motor ocuh 

 nerve. rV, fourth"nerve. "V, fifllT or trigeminal nerve. VI, sixth nerve. "VII and 

 VIII, combined rooffti facial and auditory nerves. IX and X, combined root of 

 glossopharyngeal and pneumogastric nerves. 



tions and relations of the brain during the successive stages of 

 its formation. These will be readily understood from comparison 

 of Figs. 60, 61, 64, 65, and 89. 



At the time of the first formation of the brain-tube, before 

 the hatching of the tadpole (Figs. 60, 61), cranial flexure isjerv 

 str ongly mark ed, and the fore-brain, bf, projects far in front of 

 a-ll^bt bgr organs oi' the bod y. Later_onj(Figs 64, 65),_both_ 

 these relations are changed ; the brain appears to become 



