36 

 taperiiif' gradually to the end. Its surface bears but i'ew gem- 

 aiules. 



The axone m&y arise from tlie body of the cell, or, when 

 the long a>is of the cell is horizontal, from one of the den- 

 drites. It takes a course directly for the opposite side of 

 the oblongata, giving off collaterals near its point of origin 

 and then remaining free from theni. The function of such an 

 axone is, doubtless, commissural. 



The internal structure of a commissural neurone from the 

 right side of the oblongata is drawn in ?ig.45. The cytoplasn 

 is always far less voluminous in proportion to the si^e of the 

 nucleus than in the tract-neurones. The nucleus is almost in- 

 variatly oval in outline, with its major axis disposed the 

 long way of the cell. The nucleolus is not conspicuous. The 

 chromatic material is distributed in elongated, irregularly 

 formed strands which lie throughout all parts of the nucleus. 

 The several masses may be connected with each other, but only 

 the faintest suggestion of it is indicated with the highest 

 magnification. 



The cytOf.lasm contains a considerable quantity of tigr-oid 

 substance. A few broadly triangular tigroids are scattered 

 round the nucleus, sometimes in the condition of nuclear caps. 

 The greater part of the tigroid substance is to be found at 

 the wide expanse where the cell-body merges into a dendrite. 

 Here the form of tigroid is a greatly elongated triangle. This 

 is replaced farther along the dendrite by spindle-shaped or 



