312 NERVOUS SYSTEM. 



her, and each consists of a duplication (or two layers) of the 

 membrane. They are named the J'alx and the tentorium. 



The falx or longitudinal process, so called from its being 

 resembled to the blade of a scythe (and indeed the comparison 

 is a striking one), is that expansion of the membrane which de- 

 scends for a short distance between the lobes of the cerebrum. 

 It takes its rise from the crista galli, including the projection 

 between its laminae, from which it curves forward and upward, 

 adhering in its way, first to the frontal, then to the entire length 

 of the sagittal suture, growing broader as it proceeds : at length 

 it terminates upon a thin transverse plate of bone, a process of the 

 OS occipitis anterior, where its laminae split, diverge, and end in 

 continuity with the tentorium. Whatever may be the ?/se of the 

 falx, it seems to be a part whose presence can be dispensed with, 

 for I have a cranium now before me in which it may be said to 

 be deficient ; at least, all such appearance consists in a small tri- 

 angular piece of membrane which does not project more than an 

 inch from the tentorium : and this cranium belonged to a young 

 horse who was perfectly free from any phrenetic disorder. The 

 falx is commonly said, however, to stay one lobe of the cerebrum 

 from falling or pressing upon the other when the head is inclined 

 to one side. 



The tentorium, or transverse process, is extended, after 

 the manner of an arch, from the cerebral plate of theos occipitis, 

 along the sides of the cranium, to its base ; whence, greatly di- 

 minished in breadth, it may be traced onward to the body of the 

 OS sphenoides, where it vanishes in the common covering of the 

 dura mater. It is composed of two laminae : one is continuous 

 with the falx ; the other joins that portion of the membrane 

 which covers the cerebellum. The tentorium is equally divided 

 by the falx into two lateral portions. There is some variation to 

 be seen in different subjects in the figure and extent of this pro- 

 cess, but I have not remarked that it is ever deficient. It forms 

 a transverse intersection within the cavity of the cranium, or 

 partial septum between the cerebrum and cerebellum, and ap- 

 pears to be of service in fencing these important parts in their 

 proper places, and keeping them, during the various motions and 

 positions of the head, from pressing upon each other. 



Sinuses. — These are triangular spaces, or cavities, found to 

 exist between the two layers of membrane forming the processes. 

 There are several of them. Those most worthy of notice are the 

 following : — first. 



The superior or longitudinal sinus, which runs 

 within the duplicature of the falx, along its superior border. It 

 begins in a narrow channel, gradually widening and assuming a 



