Proceedings of the Association of American Anatomists 511 



PRESENT PROBLEMS OF MYOLOGICAL RESEARCH AND THE SIG- 

 NIFICANCE AND CLASSIFICATION OF MUSCULAR VARIATIONS. 

 By Geokge S. Huntington. 



It was shown that comparative myology and the study of myological 

 variations determine three cardinal facts: 



a. Forms which, according to the zoological system commonly ac- 

 cepted, are widely separated from each other, possess identical or very 

 closely allied myological characters. 



b. Human muscular variations or supernumerary muscles are fre- 

 quenth' homologous with muscles normally present in species apparently 

 very far removed from man in the zoological scale. 



c. Within the confines of a single mammalian order, the smaller sub- 

 divisions of family and species are frequently sharply differentiated 

 from each other in some details of myological structure, which distin- 

 guishes the form possessing the modification from the remaining divi- 

 sions of the group, no matter how close in other respects their morpho- 

 logical congruence may be. In the light of more complete knowledge, 

 the commonly accepted relative phylogenetic position of many forms 

 requires revision. The fundamental mammalian type for any given 

 muscle or muscular group forms the starting point from which the 

 special difi^erentiations of the structure in the various mammalian orders 

 can be traced. - 



Human muscular variations and supernumerary muscles, as far as 

 they are rerersioiml in significance, belong to one of three classes: 

 1. Archeal Eeversions. — Not normally encountered in any mam- 

 malian type, but homologous with muscles found in the lower vertebrate 

 classes. 2. Progonal Eeversions. — Variations which are not repre- 

 sented by any normal muscle in any species composing the order, but 

 which are represented by homologous muscles in other mammalian 

 orders. 3. Ataval Eeversions. — Eeproducing muscular conditions 

 which are abnormal for the species under consideration, but which 

 occur normally in other allied species of the same order. 



THE PHYLOGENY OF LONG FLEXOR MUSCLES. By James Playfair 



McMUERICH. 



In the lower terrestrial vertebrates the flexor muscles of the forearm 

 terminate at the wrist. The ulnar and radial portions of the original 

 flexor mass early separate to form the flexores carpi ulnaris et radialis, 

 while the median portion which is inserted into the palmar fascia be- 

 comes one long flexor of the fingers. This transformation is not due to 

 the extension into the hand of the forearm flexors, but depends partly 



