PRINCIPAL REGIONS OF SPINAL CORD 89 



White substance 



Dor so-intermediate sulcus. In the kangaroo, raccoon, opossum, 

 and Java monkey, a dorso-intermediate sulcus is clearly present 

 in all three regions (figs. 8, 13, 15 and 18). In a much larger 

 number of species it is clearly evident only in the cervical region, 

 man being among this number. In some animals, the ox, sheep 

 and dog, for example, in Weigert preparations, it is not to be 

 seen in any of the regions. In most of the sections, considerable 

 difference is noted between the areas of white substance on either 

 side of this sulcus. The area nearest the dorsal median septum, 

 corresponding to the fasciculus gracilis in man, is composed of 

 relatively small, closely packed axones which give it a darkened 

 appearance in transverse sections stained by the Weigert method. 

 The lateral area which corresponds to man's fasciculus cunea- 

 tus, is composed of relatively larger axones. Singer ('81), who 

 describes the origin and position of the fasciculus gracilis in the 

 dog, shows in his drawings no septum between it and the fasci- 

 ulus cuneatus. It must be that in certain animals the factors 

 which determine whether there shall be an ingrowth of the pial 

 connective tissue to form this sulcus are different during fetal 

 life while the fasciculus gracilis and fasciculus cuneatus are being 

 acquired and becoming medullated. In most cases where the 

 sulcus is wanting, one may observe in the cervical and thoracic 

 regions that the fibers are smaller and more closely accumulated, 

 and that the area is darker, near the dorsal median septum than 

 in the more lateral areas of the dorsal funiculus. 



Position of pyramidal tract. Simpson ('02) describes the pyra- 

 amidal tract for the dog, cat and monkey as situated in the 

 dorsal part of the lateral funiculus. The guinea-pig and mouse, 

 according to Reverly and Simpson ('10), who confirm the earlier 

 work of Von Bechterew and Von Lenhossek, have the pyra- 

 midal tract in the dorsal funiculus. King ('10) has traced the 

 pyramidal tract of the rat into the dorsal funiculus. Spitzka 

 ('86) states that the sheep and ox have no fibers, to be seen 

 macroscopically, which cross from the pyramids in tl^e medulla 

 oblongata into the lateral funiculus. The elephant, according 



