GENERAL APPEARANCE OF BRAIN 437 



ENCEPHALON THE BRAIN. 



Directions. If the brain was divided into two parts, when it was 

 removed, they should be fixed together with large pins passed through the 

 cerebellum into the cerebral hemispheres ; the brain should then be placed 

 on a dissecting-room platter, with its superior surface uppermost. It is 

 necessary to keep it moist, during the whole dissection, by means of a 

 cloth dipped in water. Unless this is done the membranes are apt to 

 become dry, and then they are exceedingly difficult to remove. 



General Appearance of the Brain. When viewed from 

 above, the brain presents an ovoid figure, with the broad end 

 directed posteriorly. Its greatest transverse diameter is in 

 the neighbourhood of the part which lies between the two 

 parietal tubers of the cranium. The only portions which are 

 visible when the brain is in this position are the two convoluted 

 hemispheres of the cerebrum. These are separated from each 

 other by a deep median cleft, called the longitudinal fissure, 

 which extends from the anterior to the posterior end of the 

 brain. 



The position of the brain should now be reversed. Turn it so that it 

 rests on its superior surface. 



The inferior aspect of the brain is usually termed the 

 " base." It presents an uneven and irregular surface, which 

 is more or less accurately adapted to the inequalities on the 

 floor of the cranium. On this surface the main subdivisions 

 of the organ may be recognised. Thus, posteriorly is seen the 

 short cylindrical portion, called the medulla oblongata, through 

 which, at the foramen magnum, the brain becomes continuous 

 with the spinal medulla. The medulla oblongata rests on 

 the under surface of the cerebellum, being received into the 

 vallecula or hollow which intervenes between the two cere- 

 bellar hemispheres. The cerebellum is a mass of considerable 

 size which lies under the posterior parts of the cerebral 

 hemispheres. It can be easily recognised on account of the 

 closely set, curved and parallel fissures which traverse its 

 surface. Above the medulla oblongata, and in direct connec- 

 tion with it, is a prominent white elevation called the pons. 

 The basilar artery extends upwards in a median groove on 

 its surface. Immediately anterior to the pons there is a 

 deep hollow or recess. This is bounded posteriorly by the 

 n28 a 



