150 Journal of Comparative Neurology. 



ales. Certain of them remain nearer the mid-h'ne just ventral 

 to a seemingly attenuated commissura grisea. In sections in- 

 ferior to the decussatio pyramidum where the columnae ante- 

 riores have their natural form, these axones collect as fasciculi 

 much smaller but similar to the fasciculi cerebro-spinalis interni 

 of the elephant. They become bounded on the ventral side by 

 the commissura alba anterior in the same way as in the elephant. 

 However, they gradually decrease through the superior cervical 

 segments (quite long in the horse) and disappear in the intu- 

 mescentia cervicalis where the commissura grisea assumes the 

 more familiar form of having its two commissurae albae undis- 

 turbed by the presence of an unusual amount of medullated 

 axones between them. 



Furthermore, it appears not wholly unusual for the 

 crossed pyramidal axones to course nearer the mid-line than in 

 the lateral funiculi, though not on the ventral side of the com- 

 missura grisea nor in it. L>enhossek ('95) states that in the 

 guinea pig, the mouse, and the rat, the crossed pyramidal tracts 

 course in the ventral portion of the funiculi posteriores. In 

 the rabbit and hare (rodents also) and in the dog, cat, etc., 

 these fasciculi course in the lateral columns exclusively. In all 

 of these the pyramidal decussation as such is complete. In some 

 cases uncrossed pyramidal axones course in the funiculi laterales. 

 A ventral uncrossed pyramidal bundle (fasciculus cerebro- 

 spinalis anterior) appears, according to Lenhossek, a preroga- 

 tive of man and probably of the anthropoid apes. However, 

 in fifteen per cent, of the cases it is absent in man. There 

 were no means, of course, of determining whether the decussa- 

 tion is complete or not in the elephant. 



It has already been noted from the measurements in Table 

 II that the thickness of the funiculi laterales varies less than 

 any other feature in sections taken from the various segments 

 of the elephant. While this laterally disposed substantia alba 

 is abundant throughout the specimen, contributing to its com- 

 paratively excessive lateral diameter, its approximate constancy 

 indicates the absence of very variable components. The pyra. 

 midal tract is a variable and its presence in the lateral funiculi 



