688 THE FEATURES OF DIFFERENT REGIONS. [BOOK m. 

 sr. ir. dr. 



D2. 



Ds. 



Da. 



Sac. 



FIG. 114. DIAGRAM ILLUSTRATING SOME OF THE FEATURES OF THE SPINAL CORD 

 AT DIFFERENT LEVELS. 



All the figures are drawn to scale, and represent the cord magnified four 

 times. They shew the differences at different levels in the shape and size of 

 the cord, in the outline of the grey matter, and in the relative position of the 

 anterior and posterior fissures, and also shew the variations at different levels 

 of the several ' tracts ' of the white matter. 



C a at the level of the second cervical nerve, C 6 of the fifth cervical, C 8 of the 

 eighth cervical. D 2 of the second thoracic, D 6 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. 113 ; but in the median posterior 

 column of D 2 the areas of fibres coming from the sacral nerves s.r., and lum- 

 bar nerves l.r. are distinguished from the area, d.r. of fibres belonging to 

 the thoracic nerves. In C 8, no distinction is made between any of these 

 sets of fibres ; in L 5 only fibres of sacral nerves are represented ; in LI D 8 

 D 6 , the more dorsal small portion corresponds to sacral fibres and the next 

 to lumbar, or lumbar thoracic nerves. 



This tract, very variable in different animals, is only found in 

 the upper part of the cord ; it diminishes rapidly and soon dis- 



