Dvvight.] l^^ [March 17, 



and I) have all foui, and none of the four. Only 9.6 (I) per cent, of the 

 men have all four wanting. 



By way of a more exact method of determining what relation there may 

 be between the presence or absence of one muscle and that of the other, I 

 have put together all the cases of presence of both pyramidales, groups A, B 

 and C, into one series, and reckoned the percentages of instances of a psoas 

 parvus on both sides and on neither side, to compare them with the per- 

 centages of the normal series. 



We find 125 men and 58 women, 183 in all, having both pyramidales ; of 

 these 48 men and 16 women have the psoas parvus on both sides. Calcu- 

 lating the percentages we find that 38.4 per cent, of these men, 27.G of 

 the women and 34.9 of the whole, have the psoas parvus on both sides, 

 against 36.3, 23.5 and 32 respectively as percentages of the whole series 

 of 250. We find, therefore, that a subject with two pyramidales is a little 

 more likely to have the psoas on both sides than one which has not. The 

 next step is to take as a basis the cases of no pyramidalis, and to find 

 whether in them the percentage of psoas parvus on both sides is dlBerent 

 from that of the entire series. We find that 25 men and 23 women, 47 in 

 all, had no pyramidalis ; of these, 8 men and 4 women, 12 in all, had the 

 psoas parvus on both sides, giving percentages of 32, 18.4 and 25.5 respec- 

 tively, against 36.3, 23.5 and 33 in the entire series, showing that subjects 

 with no pyramidales are less likely to have the psoas parvus on both sides 

 than others. Thus we seem to have found a tendency, though a slight 

 one, in variations by excess and variations by defect to go together re- 

 spectively. 



By way of further comparison I have counted the number in these 250 

 subjects in which the palmaris longus was known to be absent on both 

 sides. I find this is recorded in 21 cases, and very probably occurred in 

 some others. Let us see wliether in these 21 cases there was a more fre- 

 quent deficiency of either pyramidalis or psoas minor than one would 

 expect. We find nothing of the kind. As for the pyramidalis we find it 

 was wanting in three cases only on both sides and once on one side. The 

 psoas parvus was present on both sides seven times, almost precisely the 

 percentage of the series of 250. 



Finally I found among these 250 cases, 13 in which a sternal is was 

 present on one or both sides (twice on both sides and ten times on one). 

 This is what may be called an anomaly by excess. Let us see whether 

 the series of subjects presenting it was maiked by more than ordinary 

 frequency of the pyramidalis and psoas parvus. The result is certainly 

 remarkable, for it is the very reverse of what might be expected. In these 

 12 the pyramidalis was wanting on both sides in 4, and on one side in 3, 

 leaving it therefore present on both sides in only 5. The psoas parvus 

 was more normal, being present on both sides in 5, on one side in 1, and 

 wanting in 6. If we take these two muscles together we find that both 

 were absent on both sides 3 times, a percentage of 25, which is about twice 

 that in the entire series. It cannot be denied that this series of twelve 



