174 HANDBOOK OF ANATOMY 



: sulci, which, however, are very much shallower than those of 

 the cerebrum. 



Looking at the base of the brain, it is seen that two thick cords 

 of white matter issue from the cerebrum. These are called the 

 cerebral peduncles, and joining them together is the pons 

 varolii, which is seen to consist of transverse fibres, the ends 

 of which pass into the cerebellum. Below the pons varolii is 

 the upper end of the bulb or medulla oblongata, which lies on 

 the upper aspect of the basilar process of the occipital bone. 



The medulla tapers somewhat sharply, and is continued as the 

 spinal cord. 



From each side of the pons varolii and the medulla, issue 

 the larger number of the twelve pairs of cranial nerves, which 

 supply the tissues of the head and neck. 



In transverse section the brain is seen to consist of white 

 matter with a covering about quarter of an inch thick of grey 

 matter, both of which are folded into convolutions and sulci. 

 There are also nuclei of grey matter embedded in the white. 

 The cerebellum is of similar structure. 



The brain has three membraneous coverings, named, respec- 

 tively, dura mater, arachnoid mater, and pia mater. 



The Dura Mater is a tough membrane which lines the inside 

 of the cranium, and is closely attached to it. It dips down into 

 the great longitudinal fissure, and forms a pocket, or sinus. It 

 also sends a process into the fissure between the cerebrum and 

 cerebellum, called the tentorium cerebelli, in the edges of 

 which are found sinuses. These sinuses are for the collection 

 of venous blood. 



The Arachnoid Mater is a more or less areolar structure which 

 connects the pia mater with the dura mater. 



The Pia Mater is a very thin epithelium which covers the brain 

 substance, and follows intimately all the convolutions and sulci. 

 In it numerous small bloodvessels ramify. 



Blood-Supply of the Brain. 



The blood-supply of the brain is very free, and is derived 

 from four large arteries the internal carotid and vertebral 

 arteries of each side. These enter through the carotid canal in the 



