f23 



1893.] J.^Jt» [D wight. 



subjects with sternales is too small, and yet there is some reason to think 

 that a larger series would give the same result only more strikingly. 

 Thus there are three other cases of sternalis which could not be included, 

 because in each the record of one psoas was wanting. The first had 2 

 pyramidales, one psoas was wanting, the other unaccounted for ; in the 

 second and third both pyramidales and the recorded psoas were wanting. 

 As we have found that the two sides generally agree it is probable that 

 the unrecorded psoas was in all these instances wanting. In any case if 

 these could have been added to the series they would materially have 

 diminished the frequency of psoas parvus and pyramidalis when the sterna- 

 lis was present. The criticism may be made that the sternalis should not 

 be reckoned as an instance of excessive differentiation, for it is found with 

 abnormal frequency in anencephalous foetuses and there is reason in some 

 cases at least to look upon it as a displacement of some fibres of the pec- 

 toralis major. It is to be remarked, however, that it is in these monsters, 

 rather than in adults, that the deficiency of the pectoral is common. No 

 one would think of including them in a series for the study of the fre- 

 quency of variations. In normal bodies the sternalis may, I think, be 

 called an anomaly by excess. 



These two sets of cases, namely those of absence of the palniaris longus 

 and presence of the sternalis, the latter especially, tend to disagree with 

 the conclusions reached on the series of the psoas parvus and pyramidalis. 

 None the less I am disposed to allow the series of psoas and pyramidalis a 

 certain weight. But granting that there is a tendency for variations by 

 excess and deficiency to go together respectively, the fact seems to be that 

 the tendency is a slight one and that probably the cause, whatever it may 

 be, that determines the differentiation of muscles must be considered as 

 acting in most cases on each independently of the others. 



Again the only large series of observations bearing on this point is by 

 Gruber. It deals with the psoas parvus, the palmaris longus, and the 

 plantaris of 300 subjects equally divided between the sexes. His system 

 of tabulation is not easy nor altogether satisfactory. He discusses the rel- 

 ative frequency of defect of these mascles, but apparently from rather a 

 different standpoint. In no case were all three muscles wanting on both 

 sides. In three cases only were two of them wanting in both sides and 

 one on one side. Absence of palmaris and plantaris in the same subject 

 was also verj;- uncommon. In two cases both palmares and one plantaris 

 were wanting. In no case, apparently, were both wanting on both sides. 



