THE SPIJSTAL COED.— GENEEAL. 



Among the higher vertebrates the spinal cord is found to 

 consist of nerve-cells, nerve-fihers, and a delicate connective tis- 

 sue binding them together ; while these different structures are 

 arranged in deftnite forms, so that a cross-section anywhere pre- 

 sents a characteristic appearance, the more important gangli- 

 onic nerve-cells being internal and forming a large part of 

 the gray matter of the cord. All the various regions of this 

 organ or series of organs are connected with one another, 

 white with white and gray matter, as well as white with gray 

 substance. 



While we do not attempt to furnish a complete and detailed 

 account of the anatomy of the cord or other parts of the nervous 

 system, for which the student is referred to works on anatomy, 

 we would remind him that the spinal cord is situated within a 

 bony case with joints permitting of a certain amount of move- 

 m.ent, variable in different regions. Inasmuch as the cord itseK 

 does not fill its bony covering, but floats in fluid and tethered 

 to the walls by bands of connective tissue, it is well protected 

 from laceration, bruising, or concussion. Like the brain, it has 

 a protective tough outer membrane (dura mater) with a closer- 

 fitting inner covering abounding in blood-vessels (pia mater). 



The white matter of the cord invests the horns of gray 

 matter and is made up of nerve-fibers wanting the outer sheath. 

 Here, as elsewhere, these fibers have only a conducting func- 

 tion ; they do not originate nervous impulses. The gray matter, 

 on the other hand, abounds in cells, some of them with many 

 processes, that can originate, modify, and conduct impulses. 

 Certain well-recognized groups of these cells are arranged in 

 columns throughout the cord, as shown in the accompany- 

 ing figures. The supporting basis for these cells {neuroglia) is 

 the most delicate form of connective tissue known. 



The cord may be regarded either as an instrument for the 



