358 



THE VAT. 



[CHAP, x. 



vesicles, namely, those of the mid-brain and the hind-brain. The 

 fore-brain, called also the deutencephalon, 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 mesencephalon, contains that part 

 of the primitive medullary canal, which ultimately becomes the iter 

 a tertio ad qttartum ventriculum. The corpora quadrigemina above 

 and the crura ccrebri 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 Epencephalon, and 

 this gives rise to the pons Varolii below and the cerebellum above, the 



Fig. 161. FOUR VIEWS OF THE BRAIN OF AN EMBRYO KITTEN IN THE STAGE WHERE IT FIRST 



DIVIDES INTO THE FIVE CEREBRAL RUDIMENTS SHOWING THE ACTUAL PROPORTIONS 

 OF THE PARTS. MAGNIFIED THREE DIAMETERS. 



5. Medulla oblongata, ormyelencephalon, 



0. Optic nerves. 



V. Fifth pair of nerves. 



VIII. Glosso-pliaryngeal and pneumogastric 

 nerves. 



1. Infundibulum. 



vv f . General ventricular cavity, opening ante- 

 riorly into the lateral ventricle by the fora- 



A. The brain, seen from above. 



B. From the side. 



0. Vertical section, showing the interior. 

 D. From below. 



1. Cerebral hemispheres, or prosencephalon. 



2. Region of the third ventricle the thalamen- 



cephalon or deutencephalon. 



3. Region of the corpora quadrigemina, or 



mesencephalon. 



4. Cerebellum or epencephalou. 



men of Monro. 



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

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

 sometimes called the myelencephalon or metencephaton, and this gives 

 rise to the medulla oblongata. 



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

 grows out. These together form the cerebral hemispheres, called also 

 the Prosencephalon, which give rise to the corpora striata, fornix and 

 corpus callosum. The cavity within these outgrowths are the lateral 

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

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

 foramen of Monro. 



From the anterior part of the floor of each cerebral hemisphere 

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

 nerve, called also the Rhinencephalon. Each such lobe at first like- 

 wise contains a cavity continuous with that of the lateral ventricle of 

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



The cerebral vesicles as they developc undergo a noteworthy 



