56 DISSECTION OF THE CAT 



EXTERNAL ANATOMY OF THE BRAIN. 



The brain is the portion of the nervous system 

 within the cranial cavity. It is divided into three- 

 principal parts the cerebrum, cerebellum, and 

 medulla oblongata. 



The cerebrum forms the largest part of the 

 brain, occupying the anterior portion of the cranial 

 cavity. It consists of two lobes or hemispheres. 



The cerebellum is the unpaired posterior portion 

 of the brain. It is connected with the rest of the 

 brain by bands of fibres or crura, two of which 

 pass to the cerebrum, two to the medulla, and two 

 blend together below the cerebrum and form the 

 pons Varolii. 



The medulla oblongata forms the posterior part 

 of the brain, below the cerebellum. It is continu- 

 ous posteriorly with the spinal cord. 



A. Cerebrum. 



1. The Cerebrum is the large anterior part of the 

 brain. It consists of two lobes or hemispheres, 

 which are composed of a number of convolutions, 

 or gyri, separated by fissures, or sulci. (Plate VII., 

 A, B, and c.) 



2. The Olfactory Lobes are the two small, knob- 

 like prolongations from the anterior ventral surface 

 of the cerebral hemispheres. (Plate VII., A and c.) 



3. The first pair of cranial nerves, the Olfactory, 

 arise from the under side of the olfactory lobes. 



