14 The Structure of the Spinal Cord of the Ostrich 



Between the curves which represent the grey matter and the dorsal 

 funiculi there is a closer uniformity in size; although the former shows 

 a greater increase in the regions corresponding to the wing and leg mus- 

 culature. 



Of all three curves on the diagram that of the dorsal funiculi indicates 

 the smallest as well as the least variable area. It is smallest at the 44th 

 segment, and presents practically no change as we proceed cephalad until 

 the 36th segment. If we look at Fig. 2, b it is to be seen that the dorsal 

 nerve roots from the 36th to 31st segment are enormously increased in 

 size. Corresponding to the entrance of these large dorsal nerve roots, 

 in the- same segments in the diagram there is an abrupt ascent of 

 the dorsal funiculi curve. Attention is called to the fact that the in- 

 crease in the size of the dorsal funiculi extends cephalad from the point 

 of increased dorsal root fibres. Therefore we may assume that the col- 

 laterals in the dorsal funiculi extending caudalward from the dorsal roots 

 are either very few in number or very small in diameter, and that the 

 general course of the entering impulses is in the cephalic direction. 



The descent of the curve of the dorsal funiculi from the 30th to the 

 26th segment is as abrupt as the previous ascent. While in a space of 

 six segments the area of the dorsal funiculi was increased nine times in 

 size, this area, four segments higher up, has lost already more than 

 three-fourths of this increase, and so the area at the 26th segment 

 is only one-fourth of that at the 30th. If we take for granted that 

 all the fibres that leave the dorsal funiculi enter the grey substance, 

 and that there is very little variation in the size of the fibres from the 

 30th to 26th segment (both of which facts are confirmed by microscop- 

 ical study of the cross-sections) then we may say that three-fourths of 

 the fibres present in the dorsal funiculi at the 30th segment have en- 

 tered the grey substance before the 26th segment. In other words the 

 course of the dorsal root fibres ivithin the dorsal funiculi is a short one, 

 and not more than a small proportion of these fibres ever reach the 

 medulla by this tract. 



That which is apparent regarding the dorsal funiculi in the lumbo- 

 sacral enlargement is seen again in the cervical enlargement, though in 

 the latter it is less marked. Above the cervical enlargement the rate of 

 accession and loss of fibres in the dorsal funiculi maintains a constant 

 balance, and the curve of area runs as a horizontal line. 



FINER STRUCTURE OF THE CORD. 



By the usual methods of staining, the cord resolves itself into three ele- 

 ments: Neuroglia, which forms the general framework; Nerve-Cells 



