THE DURA MATER 



28l 



the columns). There is a general division into three in each half 

 the anterior, lateral, and posterior tracts. The fibers in the anterior 

 and a portion of the lateral tracts are connected with the cells of 

 the anterior horn. They conduct motor impulses. The fibers in 

 the posterior and a portion of the lateral 

 tracts are connected with the posterior 

 horn, and conduct sensory impressions. 



All three columns contain associating A 

 fibers which connect different parts of the 

 cord with each other. These are im- 

 portant. 



MEMBRANES OF THE SPINAL CORD 



The pia mater. A delicate membrane 

 which bears the blood-vessels and is very 

 closely applied to the surface of the cord 

 (the vascular membrane of the cord). 



The arachnoid (web-like). Outside of 

 the pia mater, this has been classed among 

 serous membranes because its epithelium 

 secretes a fluid like serum; it is a single 

 fibro-serous sheet of membrane (not a 

 closed sac) which surrounds the cord 

 loosely. The fluid within it (cerebro-spi- 

 nal fluid) protects the cord from friction 

 and vibrations. 



The dura mater. A strong white 

 fibrous membrane, tubular in shape, in anterior 

 which the cord is loosely suspended. It is attached above to the 

 margin of the foramen magnum. 



The space between the dura and the arachnoid is the subdural 

 space; that between the arachnoid and pia is the subarachnoid 

 space; they contain cerebro-spinal fluid. The subarachnoid space 

 is largest in the lower portion. (The fluid in this space mixes with 

 that of the central canal through a small opening in the pia, at the 

 base of the brain.) 



The membranes are also called the meninges, and their blood- 

 vessels are the meningeal vessels. Spinal meningitis is inflamma- 

 tion of the meninges of the cord. 



FIG. 175. THREE SECTIONS 

 OP SPINAL CORD. 



A, Cervical region; B, 

 thoracic region; C, lumbar 

 region; p, posterior horn; a, 



