PINEAL GLAND. OPTIC TEAL AMI. 



579 



Fig. 393. 



extremity, as had been previously supposed by Baer, but is an expansion of the vesicle 

 downwards, in similar fashion as there is an expansion of it upwards in the region of 

 the pineal body. 



The pituitary body was asserted by Rathke to be derived 

 from a prolongation upwards of the mucous membrane of the 

 pharynx into the base of the skull between the trabeculse. It 

 appears, however, from the researches of Reichert and Bidder, 

 that the base of the skull is never imperfect in this region. 

 Reichert suggested that the pituitary body might be derived 

 from the extremity of the chorda dorsalis, but is now rather 

 inclined to think that it is a development of the pia mater. 



Fig. 393. BRAIN AND SPINAL CORD OP A FOSTUS OF POUR 



MONTHS, SEEN FROM BEHIND (from Kolliker). 



k, hemispheres of the cerebrum ; m, corpora quadrigemina 

 or mesencephalon ; c, cerebellum ; m o, medulla oblongata, the 

 fourth ventricle being overlapped by the cerebellum j s, s, the 

 spiual cord with its brachial and crural enlargements. 



The pineal gland, according to Baer, is developed from 

 the back part of the thalami, where those bodies continue 

 joined together ; but it is suggested by Bischoff that its 

 development may be rather connected with the pia mater. 

 It was not seen by Tiedemann until the fourth month ; sub- 

 sequently its growth is very slow ; and it at first contains no 

 gritty deposit : this, however, was found by Sb'mmerring at 

 birth. 



The two optic thalami, formed from the posterior part of 

 the anterior vesicle, consist at first of a single hollow sac of 

 nervous matter, the cavity of which communicates in front 

 with the interior of the commencing cerebral hemispheres, and 

 behind with that of the middle cephalic vesicle (corpora 

 quadrigemina). Soon, however, by means of a deposit taking place in their interior 



Fig. 394. 



Fig. 394. SEMIDIAGRAMMATIC VIEWS OP THE INNER SURFACE OP THE RIGHT CEREBRAL 

 HEMISPHERE OP THE FCETAL BKAIN AT VARIOUS STAGES OP DEVELOPMENT (from 

 Schmidt). 



1, 2, and 3, are from foetuses of the respective ages of eight, ten, and sixteen weeks ; 

 4, from a foetus of six months, a, lamina terminalis or part of the first primary vesicle 

 which adheres to the sella turcica ; 6, section of the cerebral peduncle as it passes into 

 the thalamus and corpus striatum ; the arched line which surrounds this bounds the great 

 cerebral fissure ; c, anterior part of the fornix and the septum lucidum ; d, inner part 

 of the arch of the cerebrum, afterwards the hippocampus major and posterior part of the 

 fornix ; e, corpus callosum, very short in 3, elongated backwards in 4 ; in 4, /, the 

 superior marginal convolution; /', fronto-parietal fissure ; g, gyrus fornicatus ; p', the 

 internal vertical fissure descending to meet the fissure of the hippocampus ; I, olfactory 

 bulb ; F, P, 0, T, frontal, parietal, occipital and temporal lobes. 



