Lectures on the Varieties in the Muscles of Man
Authors: G. M. Humphry
Journal: BMJ (1873)

the preceding lecture, I endeavoured to show that the varieties in the muscles of the trunk and neck are, for the most part, due partly to a want of proper segmentation from the simple undivided form which they present in certain of the lower animals, and partly to a want of proper concentration of the segmented portions or individual muscles into the forms which they should attain, and upon the parts into which they should be inserted, in the well developed human frame.In the present lecture, I propose to indicate that the varieties in the muscles of the upper limb, or most of them, are to be explained in the same way.The muscles which connect the upper limb with the trunk-the superior ventro-appendicular muscles-are in two sheets, derived from the two strata of the brachio-cephalic extension of the ventral muscle.The superficial sheet consists of the pectorals, the latissimus dorsi, and the trapezius, with the deltoid, which converge from a wide area upon the upper part of the humerus.The deeper sheet consists of the sub- clavius, the omo-hyoid, the levator scapulxe, and the serratus magnus.In the primitive form-that is to say, in the lower animals-the com- ponents of the superficial sheet, or some of them, extend further upon the limb, and are more blended with the several muscles of the limb, and the several component muscles of the sheet are less segmented from one another, and are more blended with the circumferential muscles, than is the case in higher animals.The sheet, indeed, in some lower animals, is a simple funnel-like expansion of the outer stratum of the ventral muscle upon the limb, extending upon the whole limb, or, at any rate, presenting no definite boundary.We are, there- fore, not surprised to find that the most important and most frequent varieties in, and in connexion with, the muscles of this sheet, are in the direction, more or less distinctly, of an approach to that simple and less segmented plan.The best examples of this-and they are also those most frequent occurrence-are the muscular additions which exhibit tendency to fill up the axillary interval, and to connect the margins the pectoralis and latissimus dorsi; though the continuity of the two muscles is rarely, if ever, so far preserved as we find it to be in Lepidosiren.*The tendency is exhibited in a variety of ways.Sometimes the range of origin of one or both muscles is extended upon the thorax, so as to approximate their edges and nearly cover the axilla.Such ex- tension is most frequent in the case of the latissimus dorsi; and this is normal disposition in many of the lower mammals.The fibres arising from this preternaturally extended area, or part of them, or, it may be, bundles of the muscle having the usual origin, often pass to the pectoral side of the axilla, constituting the axillary muscles", or the achsel-bogen" of the Germans.As many as three of these have been found in tlle same limb.tThey may blend with the pectoralis major or minor; or they may be inserted, independently of those muscles, into the coracoid, into the outer bicipital ridge Qf the humerus, or into the fascia over the coraco-brachial muscle or over the biceps.Sometimes there is merely a slip from the edge of the latissimus dorsi, * Hallett noticed this in two cases.