1905.] 



Cord of the Macaque Monkey. 



95 



By comparing the measurements of the first lumbar region with the 

 measurements of the twelfth dorsal (thoracic) given in the accompanying 

 table, it will be seen, that the increase in the section area of the cord has 

 begun prior to the region of the first lumbar nerve. 



The increase is gradual to the lower portion of the third lumbar region. 

 It becomes very marked in the fourth, for when the maximum is reached the 

 section area of the cord is more than one and a-half times as great as in the 

 first lumbar region. The section area remains very much the same 

 (19 - 5 sq. mm.) from the middle portion of the fourth to the upper portion of 

 the fifth lumbar region. The gradual decrease in section area in the 

 remaining portions of the fifth is followed by a marked diminution in the 

 sixth lumbar region. The section area in the lower portion of the sixth 

 (12 - 33 sq. mm.) is rather less than that in the first lumbar region. 

 Continuing with rapidity through the regions of the seventh lumbar and the 

 first sacral nerves, the decrease becomes more and more gradual as the lower 

 regions of the cord are reached. The section area in the lower portion of the 

 third coccygeal region is about 1 /40th that in the fourth lumbar region 

 (i.e., 0-5— 19-88 -sq. mm.). 



The section area of the grey substance (G) (Charts I, II, Table II) 

 increases from the region of the first to that of the fifth lumbar nerve, and 

 is the potent factor in the enlargement of the total section area of the 

 cord. 



The maximum (7"65 sq. mm.) is reached in the lower portion of the fifth 

 lumbar region and it is noteworthy that this is found at a lower level than 

 the maximum section areas of the cord and of the white substance. 



The grey substance decreases in section area from the fifth lumbar region 

 to the end of the cord. 



The increase in section area, though continuous, is gradual from the first to 

 the third lumbar region (lower part), becomes rapid in the fourth, and is- 

 again gradual in the fifth lumbar region. In the middle portion of the 

 fourth and the upper portion of the sixth lumbar region the section area is 

 the same (ca. 7 sq. mm.). 



The decrease is rapid from the fifth to the lower portion of the region of 

 the sixth lumbar nerve, after which the reduction of section area takes place 

 very gradually. 



In the fifth lumbar region (maximum) the section area is about three 

 times as great as that in the first lumbar region (upper part) (ca. 7'6 to 

 2 - 6 sq. mm.) ; in the second sacral it is much the same as in the first 

 lumbar, and in the third coccygeal region is about l/30th that in the fifth, 

 lumbar. 



I 2 



