THE STRUCTURE OF THE SPINAL CORD. 



551 



sr ir dr 



Sac. 



Diagram illustrating some of the Features of the Spinal Cord at Different Levels. (Sherring- 

 ton.) All the figures are drawn to scale, and represent the cord magnified four times. They show 

 the difference at different levels in the shape and size of the cord, in the outline of the gray 

 matter, and in the relative position of the anterior and posterior fissures, and also show the varia- 

 tions at different levels of the several " tracts" of the white matter. 



Q> at the level of the second cervical nerve, C 5 of the fifth cervical, C 8 of the eighth cervical. 

 Do of the second thoracic, Z> 5 of the fifth thoracic, LI of the first lumbar, L 5 of the fifth lumbar 

 and Sac. of the second sacral nerve. 



The shading of the tracts is the same as in Fig. 123; but in the median posterior column of 

 /> 2 the areas of fibres coming from the sacral nerves s.r. and lumbar nerves l.r. are distinguished 

 from the area rf.r. of fibres belonging to the thoracic nerves. In f? 8 no distinction is made between 

 any of these sets of fibres ; in L 5 only fibres of sacral nerves are represented ; in L\ D s D 5 the 

 more dorsal small portion corresponds in sacral fibres and the next to lumbar, or lumbar thoracic 

 nerves. 



are guided and coordinated. Hence, were the nervous mechanisms re- 

 stricted to the posterior horns, we should expect to find a greater parallel- 

 ism than does actually exist between them and the anterior horns. 



486. The changes in the area of gray matter illustrated by the state- 

 ments and diagrams given above refer to the gray matter as a whole that 

 is, not only to nerve-cells, but also to strands and networks of nerve-fibres 

 and nerve-fibrils, and indeed include to a certain extent neuroglia. We 

 have seen ( 479) that we are able to distinguish certain large and con- 

 spicuous nerve-cells in the gray matter, and to arrange these into groups. 



