164 Journal of Comparative Neurology. 



the medulla spinalis and the body weight of the mouse, a very 

 interesting if not accurately illustrative result is obtained. Con- 

 sidering 20 grams or 1-23 of a pound to be average weight of 

 the mouse and 8,OQO pounds that of the elephant, then if a 

 mouse of 1-23 of a pound has a medulla spinalis the area of 

 whose section is 2.8 sq. mm., a mouse with a body weight of 

 8,000 would have a section with an area 23 times 2.8 times 

 8,000, or an area of 515,200 sq. mm. instead of 432.6 sq. mm. 

 as possessed by an elephant of that weight. This number 

 divided by 432.6 will give 1,191. In other words, a mouse as 

 large as sn elephant would have a medulla spinalis, a section of 

 which in the cervical region would have an area 1,191 times 

 that of an elephant. Further, in order to have an area of sec- 

 tion 3 times that given by man, the elephant must have a body 

 weight 50 times as great as man. In order to have an area of 

 section only 3 times as great as that given by the mouse, the ele- 

 phant must have a body weight of 155 pounds or 3,565 times 

 that of the mouse. 



The above seems to indicate that the medulla spinalis of 

 the elephant must be more slender than that of the mouse and 

 such comparison as is possible shows this to be the case. 

 KoPSCH records that his specimen, exclusive of the first two 

 segments, had a length of 150 cm. In the intumescentia cer- 

 vicalis this had a mean diameter of 25.5 mm. Measurements 

 made of the corresponding portion of several mice show that 

 exclusive of the first two segments the average length of the 

 medulla spinalis is about ],.2 cm., while the average mean diam- 

 eter of the largest segment of the intumescentia cervicalis is 

 1.7 mm. If the dimensions of the medulla spinalis of the 

 elephant be reduced to a length of 3.2 cm. (that of the mouse) 

 its mean diameter will then be only about 0.5 mm. instead of 

 1.7 mm. as possessed by the mouse. 



A discussion of columns 6 and 7 is reserved for a subse- 

 quent paragraph. However, it may be here noted that the 

 area of the substantia grisea varies in the main, with the area 

 of the entire section, though the latter decreases more rapidly. 

 The ox with a heavier body than the horse has both a smaller 



