SEC. 12. THE LYMPHATIC ARRANGEMENTS OF 

 THE BRAIN AND SPINAL CORD. 



693. The Membranes of the Brain and Spinal Cord. The 

 cerebro-spinal canal is lined by a tough lamellated membrane, 

 composed of connective tissue with a small amount of elastic 

 networks, called the dura mater, which, somewhat closely adherent 

 to the walls of the cranial cavity, is separated from those of the 

 vertebral canal by a considerable space, containing blood vessels, 

 especially large venous sinuses, and some fat. It may be 

 considered as a development of the periosteum lining the 

 cerebro-spinal cavity. It sends tubular sheaths for some distance 

 along the several cranial and spinal nerves; and forms between 

 the cerebral hemispheres, in the longitudinal fissure, a conspicuous 

 sickle-shaped vertical fold, the falx cerebri, as well as a smaller 

 horizontal or oblique fold between the cerebellum and cerebrum 

 known as the tentorium. 



The vascular pia mater is closely attached to the surface of 

 the brain and spinal cord, dipping down as we have seen into the 

 ventral or anterior fissure of the cord as well as into the fissures 

 of the brain. Sheath-like investments of pia mater are continued 

 along the several nerves as they leave the cerebro-spinal cavity ; 

 and in the vertebral canal an' imperfect partition half-way between 

 the dorsal and ventral surfaces of the cord is furnished by a 

 membrane of connective tissue which, continuous along its whole 

 length with the pia mater, is attached to and fused with the dura 

 mater at intervals only, namely, between the successive nerve 

 roots. Since its outer edge has thus a toothed appearance, this 

 membrane is called the ligamentum denticulatum. Between the 

 pia mater next to the brain and cord and the dura mater next 

 to the bony walls is a cavity, which is divided into two by a 

 thin membrane, the arachnoid, composed of interwoven bundles 

 of connective tissue. The space between the arachnoid and the 

 dura mater is called the subdural space, and the space between 

 the arachnoid and the pia mater is called the subarachnoid space. 

 When the brain is exposed by removing the roof of the skull and 

 slitting open the dura mater, the subdural space is laid bare, and 

 the arachnoid is seen stretching over the pia mater; in the 



