GENERAL FEATURES 50 1 



in front of the groove between the lateral and posterior funiculi arise the 

 posterior roots of the same; a pair of roots on each side corresponding to 

 each segment of the cord. 



The nerve tracts of the cord are made up of medullated nerve fibers of 

 different sizes, arranged longitudinally, and of a supporting material of 

 ordinary fibrous connective tissue and neuroglia, figure 105. 



IS 15 



16 17 



13- 



f 

 I 



if 



FIG. 360. Horizontal Section of the Cord and its Envelopes, at the Middle of a 

 Vertebral Body (Schematic), i, Spinal cord with 2, its anterior median fissure; 3, its 

 posterior median fissure; 4, anterior roots; 5, posterior roots; 6, pia mater (in red); 7, 

 ligamentum dentatum; 8, connecting fibers passing from the pia to dura mater; 9, visceral 

 layer, and 9', parietal layer of the arachnoid (in blue); 10, subarachnoid space; n, arach- 

 noid cavity; 12, dura mater (in yellow); 13, periosteum; 13', external periosteum; 14, 

 cellular tissue situated between the dura mater and the wall of the vertebral canal; 15, 

 common posterior vertebral ligament; 16, intraspinal veins; 17, vertebra in section. 

 (Testut.) 



The general rule respecting the size of different segments of the cord 

 appears to be that each is in direct proportion in this respect to the size and 

 number of nerve roots given off from it, and has but little relation to the size 

 or number of those given off below it. Thus the cord is very large in the 

 middle and lower part of its cervical portion, whence arise the large nerve 

 roots for the formation of the brachial plexuses and the nerve supply of the 

 upper extremities; and again enlarges at the lowest part of its dorsal portion 

 and the upper part of its lumbar, at the origins of the large nerves which, 



