510 



COMPARATIVE PHYSIOLOGY. 



SPECIAI. CONSIDERATIONS. 



Embryological. — The further we progress in the study of the 

 nervous system, the greater the significance of the facts of its 



Fig. 364.— Vertical longitudinal section of brain of human embryo of foarteen weeks. 

 1x3. (After Sharpey and Eeichert.) c, cerebral hemisphere; cc, corjjas callosnm 

 beginning to pass back; /, foramen of Mnnro; jt, membrane over third ventricle 

 and the pineal body ; th, thalamus ; 3, third ventricle ; /, olfactory bulb ; eq, corpora 

 quadrigemina; cr, crura cerebri, and above them, aqueduct of Sylvius, still wide; 

 c', cerebellum, and below it the fourth ventricle; pv, pons Varolii; m, medulla 

 oblongata. 



early development becomes. It will be remembered that from 

 that uppermost epiblastic layer of cells, so early marked off in 



Fig. 365. 



Fig. 366. 



Fig. 365. — Outer surface of human foetal brain at six months, showing origin of prin- 

 cipal fissures (after Sharpey and E. Wagner). F, frontal lobe; P, parietal; 0, 

 occipital; r, temporal; a, a, o, faint appearance of several frontal convolutions; 

 s, 8, Sylvan fissure; s', anterior division of same; C, central lobe of island erf Eeil; 

 r, fissure of Kolando; ■p^ external perpendicular fissure. 



Fig. 366.— TJpper surface of brain represented in Fig. 364 (after Sharpey and E. Wag- 

 ner). 



the blastoderm, is formed the entire nervous system, including 

 centers, nerves, and end organs. The brain may be regarded 

 as a specially differentiated part of the anterior region of the 



