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 ! 

 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 



OF SPINAL CORD. 

 A, Cervical region; B, 

 thoracic region; C, lumbar 

 region; p, posterior horn; a, 



