358 



THE CAT. 



[chap. X. 



vesicles, namely, those of the mid-hrain and the hmd-hrain. The 

 fore-brain, called also the deutenccphalon, contains the anterior 

 termination of the primitive medullary canal, and this becomes the 

 third ventricle ; the pre-axial wall of the first vesicle becoming the 

 lamina terminalis of the adult. The optic thalami, optic nerves, 

 pineal gland and infundibulum, are formed from this vesicle. 



The mid-brain, called also the meHcncophalon, contains that part 

 of the primitive medullary canal, which ultimately becomes the iter 

 a tertio ad quarfum vcntriculum. The corpora quadrigemina above 

 and the crura cerebri below, are formed about this ventricle. 



The hind-brain contains the cavity of the fourth ventricle, which 

 is not all roofed over dorsally by nervous substance. The anterior 

 part of this third vesicle is sometimes called the Epencepha/o)i, and 

 this gives rise to the j^oiis Varolii below and the cerebellum above, the 



TJJI 



Fig. 161. — Potm Views of the Brain of an 



DIVIDES INTO THE FIVE CEREBRAL 

 OF THE PARTS. MAGNIFIED THREE 



A. The brain, seen from above. 



B. From tlie siile. 



C. Vertical seution, showing the interior. 



D. From below. 



1. Cerebral hemi.spheres, or proseiipeplialon. 



2. Region of the third ventricle— thu tlialauien- 



ceiilialoii or deutenceijlialon. 

 S. Region of the corpora (luadrigemina, or 



ineseiicei)halon. 

 4. Cerebellmix or eiiencephalon. 



EiiERVo Kitten in the .stage where it first 

 Rudiments — showing the actual proportions 



diameters. 



5. Jfedulla oblongata, or myelencephalon. 



o. Ojitio nt'i-ves. 



v. Fifth pair of nerves. 



VIII. Glosso-pharjiigeal and iinemnogastric 

 nerves. 



i. InfundibiUum. 



ri'. Cieneral ventricular cavity, njicning ante- 

 riorly into the lateral ventricle by the fora- 

 iiieu of Monro. 



latter arching back and covering over the hinder part of the fourth 

 ventricle. The po.sterior part of the third vesicle or hind-brain, is 

 sometimes called the miielencephalon or meiencephahn, and this gives 

 rise to the medulla oblowjata. 



From the anterior part of each side of the fore-brain another vesicle 

 grows out. These together form the cerebral //cmispl/eres, called also 

 the Frosencephalo)i, which give rise to the corpora striata, fornix and 

 corjnis calloHum. The cavity within these outgrowths are the lateral 

 ventricles, and the aperture by which they are continuous with the 

 cavity of the Deutenccphalon (or third ventricle) is the future 

 foramen of Monro. 



From the anterior ])art of the floor of each cerebral liemi.=!phero 

 yet another vesicle buds forth. This is the future olfactory lobe or 

 nerve, called also the llliinencepJialon. Each sucli lobe at first like- 

 wise contains a cavity continuous Avith Hint of the lateral ventricle of 

 its own side ; but this olfactory ventricle is obliterated in the adult. 



The cerebral vesicles as they devclope undergo a noteworthy 



