DEVELOPMENT. 



809 



TABLE OF PARTS DEVELOPED FROM FUNDAMENTAL PARTS OF BRAIN. 



I. Anterior 

 Primary 

 Vesicle, 

 or Fore- 

 brain. 



II. Middle 

 Primary 

 Vesicle, 

 or Mid- 

 brain. 

 Posterior 

 Primary 

 Vesicle, 

 or Hind- 

 brain. 



Ill 



} First Secondary Vesicle j 

 of. Prosencephalon. ] 



Second Secondary Vesicle 

 or Tha lamen cephalon 

 (Diencephalon) . 



Third Secondary Vesicle 

 or Mesencephalon. 



Fourth Secondary Vesicle 



or Epencephalon. 

 Fifth Secondary Vesicle j 



or Metencephalon. 



Anterior end of third ventricle, 

 foramen of Monro, lateral ven- 

 tricles, cerebral hemispheres, 

 corpora striata, corpus callosum, 

 fornix, lateral ventricles, olfac- 

 tory bulb. 



Thalami pptici, pineal gland, part 

 of pituitary body, third ventri- 

 cle, optic nerve and retina, in- 

 fundibulum. 



Corpora quadrigemina, crura cere- 

 bri, aqueduct of Sylvius. 



Fourth ven- 

 tricle. 



Cerebellum, pons, 

 me dulla oblon - 

 gata. 



(Quain. ) 



The cerebral hemispheres grow rapidly upward and backward, while 

 from their inferior surface the olfactory bulbs are budded off, and the 

 prosencephalon, from which they spring, remains to form the third ven- 

 tricle and optic thalami. The middle cerebral vesicle (mesencephalon) 

 for some time is the most prominent part of the foetal brain, and in 

 fishes, amphibia, and reptiles, it remains uncovered through life as the 

 optic lobes. But in birds the growth of the cerebral hemispheres thrusts 

 the optic lobes down laterally, and in mammalia completely overlaps 

 them. 



In the lower mammalia the backward growth of the hemispheres 

 ceases as it were, but in the higher groups, such as the monkeys and 

 man, they grow still further back, until they completely cover in the 



Fig. 503. Side view of foetal brain at six months, showing commencement of formation of 

 the principal fissures and convolutions. F, frontal lobe ; P, parietal ; O, occipital ; T, temporal ; 

 a a a, commencing frontal convolutions ; s, Sylvian fissure ; s', its anterior division ; c, within 

 it the central lobe or island of Reil; r, fissure of Rolando; p, perpendicular fissure. (R. 

 Wagner.) 



cerebellum, so that on looking down on the brain from above, the cere- 

 bellum is quite concealed from view. The surface of the hemispheres 

 is at first quite smooth, but as early as the third month the great Sylvian 

 fissure begins to be formed (fig. 503). 



