122 



thoracic wall ; and least frequent in the abdomen, hip, thigh, and 

 perineum. M'Whinnie, who gives a short resume of all that was known 

 in his time of these anomalies ("London Medical Gazette," N. S., 

 vol, ii. 1846), says, they are least frequent in the face and neck, then in 

 the trunk, and most frequent in the extremities — a generalization 

 which does not accord with what I have seen. In some cases the 

 order of frequency seems to depend upon the degree of specialization of 

 function uniformly enjoyed by the muscle in question in man and other 

 animals — that is, when a muscle, or group of muscles, enjoys great 

 variation of use in man, or is developed for varying purposes, and in 

 varying positions and degrees of perfection in lower animals, abnormali- 

 ties occur most frequently in it ; while a group of muscles, that in all 

 animals is devoted to one uniform use, or set of uses, is not so liable to 

 vary. Likewise, we find frequency of variation of any muscle in man 

 to be in direct proportion to the amount of divergence which that 

 muscle usually exhibits from the type muscle, as found in the majority 

 of the individuals of the animal kingdom. To illustrate these points, if 

 we look at the triceps extensor cubiti — a muscle uniformly with one 

 action — or the quadriceps extensor cruris, or the muscles of mastication, 

 we will find that they are comparatively seldom the seat of variation ; 

 while the flexors and extensors of the fingers and toes present an indi- 

 viduality in every subject which we may examine. It is likewise 

 worthy of note, that in the different regions of the body the order 

 of frequency of the different forms of muscular anomalies varies in each 

 part : thus varieties of fission are most common in the back and thorax ; 

 those of coalescence I have seen more frequently exemplified in the 

 forearm. I have illustrated this in the following diagram, in which 

 the numbers, read vertically, indicate the degree of frequency of varia- 

 tions, commencing with one which shows the most common locality for 

 the form of variation. "When a variety of any kind is very seldom 

 met with, I have marked it rare, instead of characterizing it by 

 a number : — 















Other Varie- 





Absence of 



Coales- 



New 



Fission. 



Duplica- 

 tion. 



ties, 

 Course and 





Muscles. 



cence. 



Muscle 





Germs 







Attachment. 



Forearm, 



3 



1 



1 



3 





2 



Face, . . 



2 



3f 



5 



5 



3 



5 



Back, . . 



4 



2 



6 





8 



1 



Arm, . . 



Rare. 



6 



7 



4 



5 



3 



Foot, . . 



5 



n 



3 



6 



6 



4 



Neck, . . 



Rare. 



7 



4 



2 



2 



6 



Thorax, . 



6 



4 



2 



7 



4 



7 



Abdomen, . 



1* 



8 



8 



8 



7 



8 



* Psoas parvus, pyramidaiis. 



+ Coalescence is the normal mode of insertion of some of the facial muscles, ai 

 consequently the instances used in the compilation of this table were cases of unusual umc 



+ Exclusive of the union of flexor longus digitorum and flexor hallucis longus tend* 

 which is to be found in nearly every foot. 



