FUNDAMENTAL PARTS OF THE BRAIN. 755 



and in the part behind it to be covered only by membrane, and to 

 present an opening from the cavity into the posterior sub-arachnoid 

 space. 



From what has before been said of the relation of the fundamental 

 parts of the brain to the basis of the skull, it will be seen that the 

 cerebral development is intimately connected also with the great cranial 

 flexure which occurs at the pituitary fossa ; for while the infundibular 

 prolongation of the thalaraencephalon projects down into this fossa, and 

 the lamina terminalis rises in front in the position of the original fore- 

 most part of the encephalon, certain parts of the brain may be con- 

 sidered as situated posterior to this point, viz., the mesencephalon 

 with crura cerebri, cerebellum with pons Varolii, and medulla oblongata, 

 while the cerebral hemispheres, with the corpora striata, corpus cal- 

 losum, and fornix, notwithstanding their enormous proportional de- 

 velopment, may be considered as formed by forward expansion, and as 

 situated in front of this turning point. But though the connections of 

 the cerebral hemispheres with the rest of the brain may thus be con- 

 sidered as anterior to the cranial centre, and while in their earlier stages, 

 and still of small size, they are actually placed as in the lowest Verte- 

 brates, entirely in front of it, yet by the later great proportional 

 development in the higher animals, and especially in man, the cerebral 

 hemispheres come to progress backwards, and successively to cover 

 superiorly the thalami, corpora quadrigemina, the cerebellum, and the 

 medulla oblongata. 



The connection of the several parts of the brain, with the five funda- 

 mental parts respectively, may be stated in the following tabular form : 



I" Cerebral Hemispheres, Corpora Striata, 



{1. Prosencephalon.* s Corpus Callosum, Fornix, Lateral Ven- 

 (. tricles, Olfactory bulb (Rhiuencephalou). 

 2. Thalamencephalon. f Thalami Optici,Pinealglaud,Pituitai-y body, 

 (Diencephalon.) ( Third Ventricle, Optic nerve (iirimarily). 



ir Middle urimarv Vesicle •? Mesenceiilnlon J Corpora Quadrigemina, Crura Cerebri, Aque- 

 11. -MKime primal y vesicle, o. Jiebencepiiaion. j duct of Sylvius, Optic nerve (secondarily). 



III. Posterior primary Vesicle, 



< Cerebellum, Pons Varolii, anterior part of 

 f- 4. Eiicncephalon. \ the Fom-th Ventricle. 



"j ( Medulla Oblongata, Fourth Ventricle, Au- 



1.5. Meteneephalon. ( ditory nerve. 



The changes which take place in the growth of the brain were first elaborately 

 described by Tiedemann ; they have been investigated by Von Baer, Bischoff, 

 Remak, Reichert, KoUiker, and others. (Tiedemann. " Anatomic und Bildiings- 

 geschichte des Gehu-ns," Nilremberg, 1816 ; Reichert, '' Bau des Menschlichen 

 Gehirns," Leipzig, 1859, 1861 ; F. Schmidt, '• Beitragez. Entwick. des Gehims," in 

 " Zeitschr. f. Wissen. Zool.," 1862 ; KoUiker, " Entwicklmig,sgeschichte," 1861,) 



FARTHER DEVELOPMENT OF THE BRAIN IN MAN AND MAMMALS. 



The medulla oblongata is not completely closed in above bj^ nervous matter. 

 The open part of the medullary tube constitutes the floor of the fourth rent ride, 

 which communicate.^ below with the canal of the spinal cord at the place where 

 the calamus scriptorius is eventually formed, and opens posteriorly into the 

 subarachnoid space. 



* TliLs and the four following terms are adopted as applicable to the principal secondary 

 divisions of the primordial medullary tube, and a.s corresponding to the commonly received 

 names of the German embryologists, viz., Vorderhirn, Zwischenliirn, Mittelhirn, Hinter- 

 hirn, and Nachhirn ; or their less used English translations, viz., forebrain, interbraiu 

 ('tweenbrain), midbrain, hiudbrain, and afterbrain. 



3 c 2 



