SINUSES. 377 



The veins of the brain open into these sinuses ; and the blood 

 flows through them into the internal jugular veins. They differ 

 from veins principally in this : that they are triangular, and, by 

 the tension of the dura mater, are protected from pressure. 



The principal sinuses are, 



1. The longitudinal sinus, which begins at the crista galli, 

 and, running along the upper edge of the falx until it arrives at 

 the tentorium, increases gradually in size, and terminates in the 

 two lateral sinuses. [In this sinus, and beneath the dura mater 

 near the top of the head, are many small bodies of various sizes 

 called glandulse Pacchioni. They are of various dimensions, 

 from a line and less to three or four lines in diameter. One of 

 the largest of these glands on each side protrudes through the 

 dura mater from the surface of the brain, and makes a pit in 

 the OS parietale. Vesalius demonstrated these bodies in 1543. 

 Pacchioni also demonstrated them fifty years afterwards ; and, 

 claiming them as a discovery of his own, succeeded in attaching 

 his name to them.] 



2. The two lateral sinuses run in depressions of the occipital 

 and temporal bones, until they terminate in the internal jugular 

 veins at the foramen lacerum. 



3. The torcular Herophili, which receives a large vein from 

 the interior of the brain, formed by the union of the two vena 

 Galeni, and is situated at the junction of the falx and tentorium, 

 opening into the longitudinal sinus, where it divides into the late- 

 ral sinuses. 



These are the larger sinuses of the dura mater ; but, in addi- 

 tion to these, there are several small sinuses : as, 



4. The inferior longitudinal sinus, which is situated at the 

 under edge of the falx, and receives blood from the central parts 

 of the cerebrum ; it terminates in the torcular Herophili, near 

 the beginning. The other small sinuses are situated under the 

 brain ; viz. 



5. The circular sinus of Ridley,* which frequently surrounds 

 the pituitary gland, and carries the blood from the contiguous 

 parts to the 



* An English anatomist, who flourished near the end of the 17th century. 



32* 



