122 Journal of Comparative Neurology. 



large pyramids per square mm. of cortex constituted a fair aver- 

 age.* Since there are lOO unit columns in a square mm., the 

 average number of giant cells per unit column is one tenth. In 

 two of the motor regions, 5 and 6, the giant cells occur only in a 

 small portion of the area bordering upon the anterior central gy- 

 rus. Assuming that they occur in 4% of region 5, and 2^ of re- 

 gion 6, the number'of giant cells per unit column is reduced to 

 .004 in the former case, and .002 in the latter. (Vide Table I, 

 regions 5 and 6, also Table VIII.) In region 7, giant cells are 

 found everywhere, according to Hammarberg, expect in the 

 anterior portion of the gyrus opposite the third frontal gyrus. 

 This statement agrees with the observations of Betz,^ who states 

 that the giant cells are much less numerous in the lower portion 

 of the anterior central gyrus than elsewhere. It may seem that 

 considering the giant cells as present throughout all of region 7 

 is too large a distribution. But allowing 10 to the square milli- 

 meter, is probably a small estimate for the places where the 

 cells are most numerous. These two factors, therefore, the ex- 

 tension of the area for giant cells and the small estimate of num- 

 ber for the regions where they are thickest, tend to balance one 

 another. 



By adding the number of large pyramidal cells per unit 

 column to the former calculation, the final estimate for the total 

 nnmber of cells in the various unit columns is obtained. 



' The estimate of 10 giant cells to the square millimeter is confirmed by 

 Betz (Anatomischer Nachweis Zweier Gehirncentra, Centralbl. f. d. Med. Wiss. 

 1874, Bd. XII, p. 579), where he states that the groups of giant cells are 

 placed from 0.3 to 0.7 mm. apart. Kolliker (Handbuch der Gewebelehre des 

 Menschen, 6th., Auflage. Bd. 2. Nervensystem des Menschen und der Thiere. 

 Leipzig, 1896, p. 650.) gives a cut of an enlarged section of motor cortex show- 

 ing the distribution of the giant cells. Taking the thickness of the section into 

 consideration, an enumeration of the giant cells \ix the section gives approxi- 

 mately the same result. 



» 1. c. p. 579. 



