Chap. 17.] <fhe Cerebrum and Cerebellum. 267 



of the ethmoid bone j it runs backwards along the 

 courfe of the fagittal future, to where it meets with 

 the lambdoidal. A little below the lambdoidal future 

 it divides into two wings, forming a tranfverfe feptum, 

 which is firmly attached behind to the os occipitis. 

 The ufe of the falx is to divide the brain into its two 

 hemifpheres, and to fupport them, and prevent their 

 prcfling on each other when the head is turned to either 

 fide. The tranfverfe feptum divides the great brain 

 or cerebrum from the fmaller brain or cerebellum, 

 the former being placed above it, the latter below. 

 It alfo fupports the c jrebrum, and prevents it from 

 gravitating on the cerebellum when the body is in the 

 ere<5t pofture. The connection between the tranfverfe 

 feptum and the falx is fuch, that they preferve each 

 other in a (late of tenfion, for if either of them is cut 

 after the contents of the cranium are removed, the 

 other immediately becomes relaxed and flaccid. Below 

 the tranfverfe fepcum is fituated a frnaller falx, which 

 ferves the fame purpofes in the cerebellum as the great 

 falx does in the cerebrum. In the tranfverfe feptum 

 is a great oval notch, through which the iubftance of 

 the cerebrum and cerebellum communicate and are 

 intimately mixed. 



Both the membranes of the brain pafs out of the 

 cranium with the trunks of nerves, and afford them 

 coverings, till they terminate in their fentient extre- 

 mities. 



The blood which is circulated through the brain is 

 not returned through fuch veins as are found in other 

 parts of the body. We here obferve a peculiar kind 

 of canals called fmufes, which are contained in the du- 

 plicatures of the dura mater. The mod remarkable 

 of thefe is the longitudinal, which runs in the upper 

 part of the falx ; at the tranfverfe feptum this divides 



into 



