8G ANATOMY OF THE HEAD AND NECK. 



the substantia perforata, or anterior perforated space, froi 

 being pierced by a number of openings for small arteries 

 its inner side is continuous with the lamina cinerea. 



UPPEE SURFACE AND INTERIOR OF THE CEREBRUM. 



The brain is to be turned over to bring its convexity uppermost ; 

 roll of cloth should support the whole, and elevate the anterior lol 

 so as to bring them on a level with the posterior. 



The two hemispheres are separated by a median lonj 

 tudinal fissure, at the bottom of which will be seen tl 

 broad white band of the corpus callosum. interrupting the 

 fissure at its central part, but leaving the separation ol 

 the hemispheres complete both in front and behind it. The 

 superficies of the hemispheres is marked by tortuous emi- 

 nences called gyri, or convolutions, and by intervening d( 

 pressions called sulci. Some of these convolutions have 

 been named, as, for instance, that at the bottom of the 

 median fissure, where the hemisphere rests upon the corpus 

 callosum, which is called the convolution of the corpus cal- 

 losum or gyrus fornicalus. The hemispheres of the cere- 

 brum sometimes present a want of symmet^.as to size; 

 Bichat believed this to be a condition inconsistent with a 

 perfect performance of the functions of the brain: no more 

 striking proof of the incorrectness of such a view can be 

 found than the fact that the brain of Bichat himself pre- 

 sented this very peculiarity. 



The upper part of each hemisphere is to be removed by a horizontal 

 section carried as low down as the convolution of the corpus callosum. 



The section thus made will show that each convolution 

 consists, superficially, of a layer of grayish-colored cere- 

 bral substance, lying upon a whiter structure constituting 

 the central portion of the section; the gray matter is called 

 cortical, and the white medullary. If the convexity of a 

 single hemisphere has been cut away, the medullary matter 

 of that side will be seen to have an oval shape; this is called 

 the centrum ovale minus; if both have been cut awa}^, a 

 larger medullary surface is exposed, and the two ovals will 

 be found to constitute one large oval, to which the name cen- 

 trum ovale majus is given; the surface of this section, in a 

 recent brain, is dotted with minute bloody points resulting 

 from the division of small vessels. 



The CORPUS CALLOSUM is the great commissure of the 

 brain. It is about three inches in length; its fibres are 







