THE APPENDICULAR MUSCLES. 



567 



@ 



^Dorsal muscles 



Intermuscular septum 



Mesoblastic 

 limb-core 



Post -axial 

 muscles 



•^ 



furthermore, that the muscle-fibres in succession from one border of the Hmb to the 

 other are supphed by successive nerves, those suppUed by the uppermost and, in 

 the pelvic limb at least, the lowermost nerves extending only to the neighborhood 

 of the knee (or elbow) or even a shorter distance into the limb. Thus, in the fore- 

 limb one may expect to find the more lateral muscles of the shoulder and arm 

 supplied by fibres from the uppermost nerves of the brachial plexus, those lying 

 towards the middle of the shoulder and brachial regions and in the lateral portion 

 of the antibrachium and hand regions by the middle nerves, and those along the 

 medial portion of the limb by the lower ones. In the lower limb, however, owing 

 to the rotation which it has undergone, the arrangement is to a certain extent 

 reversed, and although in the more proximal muscles the fibres are supplied by suc- 

 cessive nerves from above downward, lower. 



down the fibres from the upper nerves are Fig. 555. 



to be found along the inner side of the leg 

 and those from the lower nerves along the 

 outer side. 



If, then, an originally segmental ar- 

 rangement of the muscle-fibres of the limbs 

 is to be recognized, the segments must run 

 parallel to the long axis of the limb, and 

 this arrangement has permitted their free 

 consolidation to form the various muscles 

 found in the adult, very few indeed of 

 which are supplied by a single nerve, and 

 represent, accordingly, portions of a sin- 

 gle primitive segment. Furthermore, the 

 adaptation of the muscles to act effectively 

 on the various joints of the limbs has 

 brought about a transverse division of the 

 segments, and has also led to a complete 

 degeneration of the portions of some of the 

 segments in one part of the limb while they are retained in another. Thus, for 

 example, in the pre-axial musculature of the brachial region no trace is to be found 

 of the segments supplied by the eighth cervical and first dorsal nerves, although 

 the eighth cervical is represented in the post-axial musculature and both in the 

 pre-axial musculature of the forearm. 



On account of the occurrence of both fusion and degeneration, little trace of an 

 original segmental arrangement of the muscle-fibres is to be found in the adult limb 

 muscles, and their classification according to the segments from which they may be 

 derived is not feasible. Comparative anatomy, however, shows that primarily the 

 limb muscles were arranged with relation to the various joints of the limb, each 

 muscle, as a rule, passing over but a single joint, and in this relation may be found a 

 basis for classification. In man the original relations have been modified in many 

 cases by an alteration in one of the original points of attachment of a muscle so that 

 it passes over two joints, or by the end-to-end union of originally distinct muscles 

 so that the same result is brought about. Making allowance for these modifications, 

 however, the muscles of the upper limb may be classified into ( i ) those passing from 

 the axial skeleton to the pectoral girdle, (2) those passing from the girdle to the 

 brachium or arm, (3) those passing from the brachium to the antibrachium or fore- 

 arm, (4) those passing from the antibrachium to the carpus, and (5) the digital mus- 

 cles. Similarly in the lower limb, in which, however, owing to the firm articulation 

 of the pelvis to the sacrurri, the first group of muscles is practically unrepresented, 

 or at least may be placed with those of the second group extending from the pelvic 

 girdle to the femur. With this grouping there may be combined a recognition of 

 the pre-axial and post-axial musculature, these terms being used in the lower limb as 

 well as in the upper to indicate the relationships which obtained before the rotation 

 of the limb. 



Diagram of pre- and post-axial groups of limb-muscles. 

 {Kollmann.') 



