Uli: ORGANS <>l 1111. (.1 II. K .l I 



125 



! of tin- cerebellum and that of the after-brain, and lm> tin- 

 form of a ridge which projects Neutrally fr a con-ideraMe di-taiiee, 

 where subsequently the transverse libivs "f tin- p>ns Yaml 

 I'lished. 



The extent of tin-so curvatures is very different in tin- \ 



f Vertebrates. Thus the cephalic llexuro is only slightly 

 empha.-i-ed in the lower Vertebrates (Cyclostomes, Fishes, Amphibia] ; 

 it i>. cm the eoni rii-y. nuich greater in lloptilos, I'.irds. ami Mammal- ; 

 but in Man especially, whose brain is the most voluminous, all of tin* 

 ilex u res are developed to a very high deg 



The live hraiii-veMi-les furni>h tin- foundation for a natural >ub- 

 di\i>ion of the brain, whose various chief divisions can be ref- 

 back to them. As the study of the further development teaches, 

 then- are formed from 

 the after- brain vesicle 

 the medulla oblongata, 

 from the vesicle of the 

 cerebellum the vermi- 

 form process with the 

 hemispheres of the cere- 

 bellum and the pons 

 Yarolii, from the mid- 

 brain vesicle the crura 

 cerebri and corpora 

 quadrigeinina, from the 

 between - brain vesicle 

 the bet we en-brain 



[thalamencephalon] with the infimdibulum, the pineal gland, and the 

 optic thalami, and finally from the vesicle of the cerebrum the 

 cerebral hemispheres. 



Tn this metamorphosis the cavities of the primitive cerebral tube 

 me the so -call- ^es of the brain : from the cavities of the 



fourth and tilth vesicles i> derived the fourth ventricle or fossa 

 rhomboidalis ; from the cavity of the mid-brain vesicle, the aque- 

 duct of SYLVIUS; from tke between- brain, the third ventricle; and 

 finally from the cavities of the hemispheres, the i\\- lateral 

 which are also designated as the first and >ec,md ventr: 



A brief sketch will suffice to show in what manner the most 

 important parts of the brain develop out of the live vesicular 

 fundaments, and that at the same time histological and morphological 

 ilillerentiations are most intimately associated. 



Fig. 239. Brain of a Rabbit embryo 16 mm. long, viewed 

 from the left side. The outer wall of the left cerebrum 

 is removed 



tn, Optic nerve ; ML, foramen <>i Mvuo ; agf, fold of the 

 choroid plexus ; amf, fold of the coma Ammonia ; 

 r/i, bet ween -brain ; iiih, mid-brain (cephalic or pa: 

 ili-xure) ; kh, cerebellum ; Dp, roof -plate of the fourth 

 ventricle ; 66, pontal flexure ; io, medulla oblongata. 



