298 MANUAL OF HISTOLOGY. 



tern, contains some blood-corpuscles and swollen epithelial 

 cells. 



General histology of the spinal cord. The spinal cord is 

 composed of connective tissue, blood-vessels, nerve-structures, 

 and epithelium. 



The connective-tissue framework or neuroglia of the cord 

 is constructed as follows : At tolerably regular intervals the 

 pia mater at the periphery of the cord sends off prolonga- 

 tions which form septa, dividing the white substance into a 

 large number of prisms (base outward). From each of these 

 septa smaller branches spring, forming a delicate network, or 

 stroma, which encloses the nerve-fibres. Generally one, but 

 sometimes two or more fibres are contained in the same mesh. 



At the points of junction of these ultimate fibres are seen, 

 here and there, small branching cells, the so-called spider- or 

 neuroglia-cells. This fibrous structure reaches to the central 

 gray matter and penetrates it by very delicate processes, which 

 chiefly accompany the nerve-fibres. 



Three large prolongations of pia mater are of constant oc- 

 currence, viz., the posterior median septum and a less complete 

 septum on either side, dividing the posterior column into two ; 

 the larger, anterior, or column of BurdacJi ; and the smaller, 

 posterior, or column of Goll. The connective-tissue elements 

 are best brought out by hsematoxylon. 



The blood-vessels of the cord are derived froni its pia mater, 

 follow its prolongations, and are most numerous in the gray 

 matter, especially that of the anterior horns. In transverse 

 sections there will be seen a clear space about all the blood- 

 vessels. This is the perivascular space or lymph-channel, in 

 which all the blood-vessels are contained. During life these 

 sheaths probably serve a double purpose : an auxiliary nutri- 

 ent function by lymph-circulation ; and a means of accommo- 

 dating the ever-varying degrees of vascular distention. In 

 some diseases they become enormously dilated. They are all 

 connected with the space between the pia mater and the cord, 

 and an injection forced into this space will follow the blood- 

 vessels for long distances. These perivascular spaces are also 

 said to be lined with endothelium. 



The vessels of the cord present no other peculiarities. Their 

 structure is best brought out by the use of a dilute htematox- 

 ylon solution, or by the slow carmine staining. The perivas- 



