CHAPTER XIV. 



THE NERVOUS SYSTEM Continued. 



144. Structure of the Encephalon. The brain or ence- 

 phalon, the portion of the cerebro-spinal axis contained within 

 the cranium, consists of various parts to which different names 

 are given. The part in continuity with the spinal cord, as has 

 already been mentioned, is called the medulla oblongata. It 

 is about an inch and a quarter long, and broadened above, and 

 in it both the white and grey matter have a different arrange- 

 ment from that existing in the cord. In front are the 

 columns called anterior pyramids, whose decussation has 

 already been mentioned; outside these are the olivary bodies, 

 each containing a grey centre of unknown function; while 

 outside these are two stout pillars called restiform bodies, 

 including the posterior half of the lateral columns of the 

 cord, and all the fibres of the posterior columns with the 

 exception of two small bands behind, distinguished as pos- 

 terior pyramids. These and the restiform bodies slope out- 

 wards as they ascend, and limit at the back of the medulla 

 oblongata a groove lined with grey matter, continued up 

 from the central canal of the spinal cord. This groove 

 forms the floor of what is called the fourth ventricle of 

 the brain, a space between the medulla oblongata and the 

 cerebellum. 



Above, the medulla oblongata is crossed in front by a thick 

 transverse band, called the pons Varolii, which conceals the 

 continuation of the fibres of the medulla upwards to the 

 cerebrum, and sends its fibres into the cerebellum on each 

 side. Below them the restiform bodies enter the cerebellum, 

 and thus are formed what are called the middle and inferior 

 crura cerebelli; while the superior crura are a pair of bands 

 which pass from the cerebellum to the cerebrum. All the 



