96 Journal of Comparative Neurology and Psychology. 



in section to those of the ostrich as described by Streeter. 

 For this reason the description of these parts of the emu cord 

 may be omitted here. 



That the segmental enlargements are morphologically so 

 evident in the emu cord is no doubt to some extent due to the 

 great length of its segments. Were the segments as short rela- 

 tively as they are in the mammals, the swellings would tend to 

 merge one into the other and be less noticeable. However, it 

 must be conceded that morphological segmentation at least is 

 more marked in the spinal cords of birds and their relatives, 

 the reptiles, than in the higher vertebrates. It is of interest 

 as indicating the position of the birds in the animal scale. It 

 is more marked in the still lower vertebrates, and in the in- 

 vertebrates, the general rule is that the central nerve axis con- 

 sists simply of a ganglionic chain, distinct ganglia for each body 

 segment, while swellings opposite each pair ot nerves are indi- 

 cated in the early development of all vertebrates. 



Segmental swellings in the spinal cords of the lower verte,- 

 brates have be^n long observed. Luderitz ('81) notes that 

 Collins described such enlargements at the levels of the attach- 

 ment of the nerves in fishes as early as 1685. Later such con- 

 ditions in the fishes, especially the Triglidae, have been fre- 

 quently mentioned. Carus ('14) was the first I think to dis- 

 cuss their functional significance. He also described them for 

 the spinal cord of the snake. Luderitz pictures segmental 

 enlargements in the spinal cord of the ringed snake {Tropido- 

 notiis natnx) and also shows that such are indicated in the cer- 

 vical segments of the rabbit. Further, by comparing transverse 

 sections taken at different levels of the segments, he thought it 

 indicated in the human spinal cord also. Numerous publica- 

 tions have since appeared supporting in general the views of 

 these earlier writers. 



The tendency of the ventral horn cells to cluster toward 

 the levels at which the nerves are atached, also has a rather 

 voluminous literature. It is of course very evident in those 

 animals (fishes, etc.) having very marked segmental swellings. 

 Stieda ('68) may be mentioned among the first to study it in 



