846 



DEVELOPMENT. 



[CH. LVIII. 



TABLE OP PAETS DEVELOPED PROM FUNDAMENTAL PARTS OP 

 BRAIN. 



I. Anterior 

 Primary 

 Vesicle. 



r Anterior end of third ventricle, 



First Secondary Vesicle, 

 Prosencephalon, 

 Fore-brain. 



Second Secondary Vesi- 

 cle, Thalamencepha- 

 lon, or 'Twixt-brain. 



II. Middle ( Third Secondary Vesicle, 

 Primary \ Mesencephalon, or 

 Vesicle. ( Mid-brain. 



r Fourth Secondary Vesi- 



T TT r> i. cle, Epencephalon, or 



III. Posterior I Hind _ rain> P 



i-nmary Fifth Secondary Vesicle, 

 Metencephalon, % or 

 v After-brain. 



foramen of Monro, lateral ven- 

 tricles, cerebral hemispheres, 

 | corpora striata, corpus callosum , 

 fornix, lateral ventricles, olfac- 

 v tory bulb. 



( Thalami optici, pineal gland, part 

 I of pituitary body, third ven- 

 | tricle, optic nerve and retina, 

 \. infundibulnm. 



/ Corpora quadrigemina, crura 

 \ cerebri, aqueduct of Sylvius. 



{Cerebellum and 

 Pons. 

 Medulla oblon- 



tricle. 



The cerebral hemispheres grow rapidly upwards and backwards, 

 while from their inferior surface the olfactory bulbs are budded 

 off. The middle cerebral vesicle (mesencephalon) for some time 

 is the most prominent part of the foetal brain, and in fishes, 



Fig. 665. Side view of foetal brain at six months, showing commencement of formation 

 of the principal fissures and convolutions. F, frontal lobe ; P, parietal ; 0, occipital : 

 T, temporal ; a a a, commencing frontal convolutions ; s, Sylvian nssure ; *', its 

 anterior division ; c, within it the central lobe or island of Reil ; r, nssure of Rolando ; 

 p, parieto-occipital nssure. (R. Wagner.) 



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

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

 tnrusts the optic lobes down laterally, and in mammalia com- 

 pletely overlaps them. 



In the lower mammalia the backward growth of the hemi- 

 spheres ceases, but in the higher groups, such as the monkeys 



