chap, xvi.] THE SPINAL CORD. 127 



occasionally embedded in a granular-looking material, 

 and thereby a similar organ as the nerve endplate of 

 muscular fibres is produced (Fig. 80). (c) A medul- 

 lated nerve-fibre terminates in an end-bulb (Fig. 81), 

 similar to those of the conjunctiva, or of a Herbst's 

 corpuscle. 



CHAPTER XVI. 



THE SPINAL CORD. 



162. THE spinal cord is enveloped in three distinct 

 membranes. The outermost one is the dura mater. 

 This is composed of more or less distinct lamellae of 

 fibrous connective tissue with the flattened connective 

 tissue cells and networks of elastic fibres. The outer 

 and inner surface of the dura mater is covered with 

 a layer of endothelial plates. 



163. Next to the dura mater is the arachnoid 

 membrane. This also consists of bundles of fibrous 

 connective tissue. The outer surface is smooth and 

 covered with an endothelial membrane facing the 

 space existing between it and the inner surface of the 

 dura mater ; this space is the sub-dural lymph space. 

 The inner surface of the arachnoidea is a fenestrated 

 membrane of trabeculse of fibrous connective tissue, 

 covered on its free surface i.e., the one facing the 

 sub-arachnoidal lymph space with an endothelium. 



164. The innermost membrane is the pia mater. 

 Its matrix is fibrous connective tissue, and it is lined 

 on both surfaces with an endothelial membrane. 

 Between the arachnoid and pia mater extends, from 

 the fenestrated portion of the former, a spongy plexus 

 of trabeculse of fibrous tissue, the surfaces of the 

 trabeculse being covered with endothelium. By this 



