THE NERVOUS SYSTEM. 295 



or crusta, and the posterior portion, or tegmentum, between which is a 

 mass of gray matter the locus nlger; 



Pons Varolii, covers up the posterior portion of the cerebral lobes. 



INTERIOR OF THE CEREBRUM. The interior of the cerebrum, 

 viewed above the level of the corpus callosum, presents a white 

 surface the centrum ovale minus, the margins of which are con- 

 voluted gray matter, and are called labia cerebri. It is studded 

 throughout with minute blood-vessels puncta vasculosa. 



The hemispheres, viewed on a level with the corpus callosum, 

 present a large white mass the centrum ovale majus in the 

 centre of which is the connecting band, the corpus callosum. 



Corpus Callosum. This connecting band forms the roof of 

 the lateral ventricles. It is about four inches in length and 

 varies from an inch and a half to two inches in width, presenting 

 in front a bend, or genu, below which it terminates in the tuber 

 cinereum through the lamina cinerea. 



Posteriorly it forms a thick, rounded fold the splenium, 

 or pad which is continuous with the fornix. 



The peduncles of the corpus callosum are two reflected bun- 

 dles of white matter given off near the anterior termination of 

 the corpus, and each passing backward across the anterior per- 

 forated space of its own side to the fissure of Sylvius. 



The superior surface of the corpus callosum shows a depres- 

 sion the raphe bounded on each side by elevated bands, the 

 striae longitudinal es, or nerves of Lancisi. External to these 

 are the strice longitudinales laterales. On either side of the raphe 

 are many transverse lines the lineas transversse, which indicate 

 the direction of the fibres of the corpus. 



THE CEREBRAL COMMISSURES are connecting bands of gray 

 and white matter, pursuing either a transverse or antero-posterior 

 course. 



Transverse: 



Anterior, middle, and posterior commissures; 



Corpus callosum; 



Optic chiasm ; 



Fornix ; 



Pons Varolii: 



Posterior medullary velum. 



Antero-posterior: * 



Corpus callosum (nerves of Lancisi) ; 

 Fornix; 



Fasciculus uncinatus; 

 Tnenia semicircularis; 

 , Gyrus fornicatus; 



