364 DURA MATER PROCESSES. 



of dura mater descending between the hemispheres, and if he draw 

 one side of the brain a little outwards, he will distinctly perceive its 

 extent; this is the falx cerebri. 



The processes of dura mater which are sent inwards towards the 

 interior of the skull, are the falx cerebri, tentorium cerebelli, and 

 falx cerebelli. 



The Falx cerebri (falx, a sickle), so named from its sickle-like 

 appearance, narrow in front, broad behind, and forming a sharp 

 curved edge below, is attached in front to the crista galli process of 

 the ethmoid bone, and behind to the tentorium cerebelli. 



The Tentorium cerebelli (tentorium, a tent) is a roof of 'dura 

 mater, thrown across the cerebellum and attached at each side to 

 the margin of the petrous portion of the temporal bone, behind to 

 the transverse ridge of the occipital bone, which lodges the lateral 

 sinuses, and to the clinoid processes in front. It supports the poste- 

 rior lobes of the cerebrum and prevents their pressure* on the 

 cerebellum, leaving only a small opening anteriorly, for the trans- 

 mission of the crura cerebri. 



The Falx cerebelli is a small process, generally double, attached 

 to the vertical ridge of the occipital bone beneath the lateral sinus, 

 and to the tentorium. It is received into the indentation between 

 the two lateral lobes of the cerebellum. 



The layers of the dura mater separate in several situations, so as 

 to form irregular channels which receive the venous blood. These 

 are the sinuses of the dura mater; they are described at page 331, 

 in the Chapter on the Veins. 



The student cannot see the. tentorium and falx cerebelli until the 

 brain is 'removed; but he should consider the attachments of the 

 tentorium upon the dried skull, for he will have to divide it in the 

 removal of the brain. He should now proceed to that operation, 

 for which purpose the dura mater is to be incised all round, on a 

 level with the section through the skull, and the scissors are to be 

 carried deeply between the hemispheres of the brain in front, to cut 

 through the anterior part of the falx ; then draw the dura mater 

 backwards, and leave it hanging by its attachment to the tentorium. 

 Raise the anterior lobes of the brain carefully with the hand, and 

 lift the olfactory bulbs from the cribriform fossae with the handle of 

 the scalpel. Then cut across the two optic nerves and internal 

 carotid arteries. Next divide the infundibulum and third nerve, and 

 carry the knife along the margin of the petrous bone at each side, 

 so as to divide the tentorium near its attachment. Cut across the 

 fourth, fifth, sixth, seventh, and eighth nerves in succession with a 

 sharp knife, and pass the scalpel as far down as possible into the 

 vertebral canal, to sever the spinal cord, cutting first to one side 

 and then to the other, in order to divide the vertebral arteries and 

 first cervical nerves. Then let him press the cerebellum gently for- 



* In leaping animals, as the feline and canine genera, the tentorium forms a bony 

 tent. 



