THE NERVOUS SYSTEM.^ 113 



to moisten the brain ; and furnish a medium o-transmitting 

 blood vessels and absorbents^ 



8. |The outside surface of the brain is cut up, or inter- 

 sected by deep winding fissures, forming numerous irregular 

 eminences called convolutions. These fissures are generally 

 about an inch deep.) The brain on the outer surface, is to a 

 considerable depth of a grey or ash colour ; (hence it is called 

 me cineritious or ashy portion, and sometimes cortical, from 

 its position, like the bark surrounding a tree. The internal 

 portion is white, and is therefore called the medullary part of 

 the brain| 



9. (The cortical part of the brain which is found on the 

 exterior surface, is on an average about one-sixth of an inch 

 in depth, and dips down every where between the convolu- 

 tions.v Besides its being of a greyish colour, it is of a firmer 

 consistence than the medullary matter. It is full of vessels, 

 and from this circumstance has been supposed to nourish the 

 medullary part. 



10. *There are four cavities in the substance of the brain, 

 termed ventricle^ Of these the two lateral ventricles are the 

 largest. During life a serous exhalation is constantly going 

 on into their interior, and in health this fluid is absorbed or 

 taken up, as fast as it is secreted. In dropsy of the brain, 

 the water sometimes accumulates in these cavities in im- 

 mense quantities. Not long since, a child, about ten years 

 of age, was exhibited in this city, whose head measured two 

 feet and seven inches in circumference, just above the ears. 

 The head was so heavy he could not raise it from the pil- 

 low. This was owing to water in the ventricles. The med- 

 ullary or white matter of the brain occupies the interior part 

 of that organ. It makes up by far the largest portion, and 

 is fibrous in its structure. 



11. rThe cerebellum or little brain, is situated at the base 

 and back part of the skull, and in weight it is only about one- 

 eighth or ninth part of that of the cerebrum. Like the large 

 brain, it is divided into two lateral halves. It is made up of 



10* 





