58*2 HANDBOOK OF PHYSIOLOGY. 



matter divided by fissures into convolutions (fig. 354) , and covering to a 

 large extent the other parts, separated from one another by a deep 

 fissure running from front to back. These constitute the cerebral 

 hemispheres or cerebrum, (b) On the under or central surface of the 

 brain can be seen a broad mass rounded on the surface more or less 

 quadrilateral in shape; this is the pons Varolii (fig. 354, VI.) . Aii- 



Fig. 354. Base of the brain. 1, superior longitudinal fissure; 2, 2', 2", anterior cerebral 

 lobe; 3, fissure of Sylvius, between anterior and 4, 4'. 4", middle cerebral lobe; 5, 5', posterior 

 lobe; 6, medulla oblongata. The figure is in the right anterior pyramid; 7, 8, 9, 10, the cerebellum ; 

 -f- , the inferior verimf orm process. The figures from I. to IX. are placed against the corresponding 

 cerebral nerves; III. is placed on the right crus cerebri. VI. and VII. on the pons Varolii; X. 

 the first cervical or suboccipital nerve. (Allen Thomson.) J 



teriorly it is seen to branch off into two strands, which are the crura 

 cerebri; and posteriorly it joins with a narrower portion, which is the 

 medulla oblongata or bulb. This latter is continuous with the spinal cord. 

 In connection with the bulb and pons are seen many nerve-trunks pass- 

 ing off; these are the chief part of the cranial nerves. Two of the 

 cranial nerves, however, are more interior, and one, the optic (fig. 354, 

 2), is seen to send off a broad band of fibres which apparently passes 

 into the substance of the cerebrum. The most anterior nerve-root on 

 either side, viz., the olfactory (fig. 354, 1), extends for some distance 

 upon the under surface of each cerebral hemisphere, (c.) The pons is 

 seen to be connected laterally with a large mass of nervous matter, upon 

 which in the position of the brain turned upward, the bulb also rests j 



