of it which lies forward. The hinder part (conside- 

 rably smaller) is called the cerebellum. Under both, 

 but chiefly the latter, and springing from the internal 

 substanee ofboth, is the medulla oblongata. 



The skull is divided into two plates, one laid over 

 the other. Between these is a spongeotis substance, 

 made of boney fibres detached from each plate. 

 Hereby the skull is made not only lighter, but far less 

 liable to fractures. 



The skull is covered with a membrane called the 

 pericranium. This has several holes, which, give 

 passage to the spinal marrow, the nerves, arteries^ 

 and veins. But these fill them so nicely, that nothing 

 can pass into or out of the head, but through these 



It is round, that it may contain the more ; but a 

 little depressed and longish, advancing out behind, anc} 

 flatted on the sides, which contributes to the enlarge- 

 ment of the sight and hearing. 



It is divided into pieces by four sutures. This 

 makes it less liable to break, gives passage to the 

 membranes of the pericranium, and vent to the matter 

 of insensible perspiration . 



18. All these are involved in two membranes, the 

 inner (called pia mater) extremely thin, the outer 

 ^called dnra mater) considerably harder and thicker. 

 Where tlicy involve tl*e cerebellum, there is inter- 

 posed between them the araclmoides,a Tery subtle and 

 transparent membrane, which descending through the 

 hinder part of the skull, together with them involves 

 the whole spinal marrow. 



19. The outer part of the brain (called the cortex 

 or bark) Is of an ashy or greyish colour. It is form-* 

 ed from the minute branches of the neighbouring ar- 

 teries, which being wove together in the pia_,pter, 

 enclose the inner part, ordinarily to the thickness of 

 about half an inch. 



It consists, therefore, of innumerable little glands, 

 c 4 



