Hardesty, Medulla Spinalis of the Elephant. 149 



doubt, in the substantia grisea of one side and cross over to the 

 other side as components of the commissura alba anterior as in the 

 medulla spinalis. In passing into the medulla spinalis, the fasciculi 

 seen to arise from the decussatio pyramidum become more 

 compactly bundled and the trabeculae become condensed into 

 the commissura anterior as found in lower segments. As 

 compared with the more common mammals, this commissure 

 appears displaced ventrally, an appearance resulting from the 

 accumulation of these pyramidal axones on its dorsal side. The 

 result is consequently that two longitudinal fasciculi are isolated, 

 one on either side of the mid-line and so enclosed as to appear 

 situated within the commissura grisea between its anterior and 

 posterior commissurae albae. 



Therefore, it is assumed that the internal or enclosed fasci- 

 culi found in the medulla spinalis of the elephant are composed 

 of crossed pyramidal axones, and thus each may be classed as 

 that fasciculus which in man is situated laterally and which is 

 called "fasciculus cerebro-spinalis lateralis" or crossed pyra- 

 midal tract. This being true, this internal fasciculus of the 

 elephant may be designated as -'fasciculus cerebro-spinalis in- 

 tern us" [F. c. i.. Figs. 5, 8 and 12). Its isolation is the result 

 of its position. 



In having its crossed pyramidal tracts situated mesially in- 

 stead of laterally the elephant is not wholly unique. For the 

 purpose of making some comparative studies of sections from 

 the intumescentia cervicalis, material was obtained from several 

 of the common but infrequently studied mammals. In addition 

 to the sections from the required cervical segment, sections 

 were also made from the medulla oblongata of several of these. 

 Among them was the horse. The medulla oblongata of this 

 animal proved a very interesting subject in itself. Its descrip- 

 tion will not be taken up here further than to say that the mass 

 of pyramidal axones seems great, and that their decussation in 

 the medulla oblongata is so marked and localized as to entirely 

 obliterate all suggestion of the form of the columna anterior. 

 Yet it appears from a study of several serial sections that all of 

 the decussating axones do not pass over into the funiculi later- 



