2IO ELEMENTS OF MAMMALIAN ANATOMY 



ing SO closely the folds and clefts of the brain that it becomes 

 apparent only when lifted carefully by the forceps. 



In order to study the brain satisfactorily each student should 

 have a specimen hardened according to directions on page 14, 

 and also should be permitted to examine a series of sections cut 

 transversely about a centimeter thick. The brain of a calf or 

 sheep serves the learner's purpose better than that of a cat, as 

 the parts are larger, and they are also easier to procure. An 

 additional advantage is also found in the fact that there is some 

 difference between the brains of the cat and calf, and the 

 student must therefore rely more on his own observations. 



External Features.^ — The brain is composed of five parts: 

 the medulla oblongata, or myelencephalon; the pons Varolii and 

 cerebellum, forming the meiencephalon; the corpora quadri- 

 gemina and crura cerebri, composing the mesencephalon; the 

 diencephalon, including the optic thalami and other parts 

 bounding the third ventricle; and the telencephalon, or cerebral 

 hemispheres. The medulla oblongata, sometimes called the 

 bulb or stem of the brain, is the expansion of the spinal cord as it 

 passes through the foramen magnum. The pons Varolii is the 

 bridge of transverse fibers seen on the ventral aspect of the 

 brain just craniad of the medulla (Fig. 104). The cerebellum or 

 little brain lies on the dorsal side of the medulla and is partly 

 covered by the caudal part of the cerebrum. The mesencephalon 

 is not visible externally on the dorsal aspect, but may be seen 

 immediately craniad of the cerebellum by cutting away the 

 cerebrum (Fig. 107). The diencephalon is visible externally only 

 on the ventral aspect of the uncut brain, where it forms the floor 

 of the third ventricle. It may be viewed as a whole if the dorsal 

 half of the cerebrum including the corpus callosum is cut away. 

 The telencephalon or end brain is composed of the two large 

 hemispheres partially surrounding the diencephalon and 

 mesencephalon. 



The brain is composed of two kinds of matter, white and gray. 

 The former is constructed for the most part of fibers, while the 



