MEMBRANES OF THE BRAIN. 341 



on each side, so that a deep depression is formed for lodging 

 the pituitary gland. 



The Falx Cerebelli is a small triangular process of the dura 

 mater, which extends in the middle line from the under surface 

 of the tentorium to the posterior margin of the occipital fora- 

 men. Its base is above, and its point below: the latter termi- 

 nates by a small bifurcation. It adheres by its posterior mar- 

 gin to the middle inferior limb of the occipital cross; the ante- 

 rior margin is free, and serves to separate the two hemispheres 

 of the cerebellum. 



The Dura Mater is essentially fibrous, as is sufficiently evi- 

 dent at whatever point it may be examined. These fibres have 

 no settled cou/se, but cross each other in every direction. It 

 is white, sufficiently transparent for the vessels of the pia ma- 

 ter to be imperfectly seen through it, and almost inelastic. Its- 

 internal face is smooth and polished, and is covered or lined by 

 the tunica arachnoidea, the halitus from which gives it a slip- 

 pery feel. It is insensible to common excitants, such as cutting, 

 or even cauterizing it ; from which circumstance, together with 

 the common inability of anatomists to trace nerves into its 

 structure, it is supposed, by many, to be entirely destitute of 

 them. The venerable Chaussier, however, takes a different 

 position in regard to these points, and says, that it has sensibi- 

 lity, and that though none of the cerebral nerves can be traced 

 into it, yet, by attentive examination, it is found, that filaments 

 from the sympathetic nerve follow the ramifications of its mid- 

 dle or great artery.* 



It is well supplied with blood vessels, both arteries and veins. 

 The former are derived principally from the branches of the in- 

 ternal maxillary of either side, which get into the cranium 

 through the foramen spinale and ovale. There are branches 

 also from the ethmoidal, the inferior pharyngeal, and the ver- 

 tebral. The branch of the internal maxillary called meningea 

 magna divides into two, of which the anterior being the more 

 considerable, gains the anterior and inferior angle of the parie- 

 tal bone; but the other is directed backwards to the squamous 



* Exposition de L'Encephale, p. 29, 

 30* 



