464 



tative, not of the rectus femoris, but of the hamstrings of the lower 

 extremity ; the long head representing, doubtless, the origin of the semi- 

 membranosus, which is typically placed nearer to the articulation than 

 either of its congeners, and which also is the more external and most 

 tendinous at its origin. The coracoid, or short head, thus may repre- 

 sent the ordinary long head of the biceps cruris ; and the humeral acces- 

 sory slip in the arm, when present, is the evident homologue of the short 

 head of the last-named muscle. In a few of the Quadrumana I have 

 been able to separate the heads of the biceps in a similar manner. 



In this representation of the homotypical relations of the flexors of 

 the leg and forearm* it will be seen that! have differed materially from 

 Meckel's theoretical comparison of these muscles ; as this anatomist, 

 from the occasional occurrence of a connecting band between the coraco- 

 brachialis and the brachialis anticus, has considered that these muscles 

 are parts of a modified representative of the semimembranosus, divided 

 transversely in the midst, and having both its severed ends tacked on 

 to the shaft of the humerus. There are, however, many valid objec- 

 tions to this explanation, as it would make the representative of the semi- 

 membranosus to arise internal to the other flexors, which is usually not 

 the case with that muscle ; also that it is never united with the biceps at 

 its origin ; and, lastly, that it usually arises by a tendon, and not fleshy; 

 besides, as we shall see hereafter, the coraco-brachialis may claim a 

 closer relation to another class of muscles than to the hamstrings. 



5. The deltoid muscle is sometimes completely divided into two parts, 

 clavicular and scapular. I never, however, have seen the fission extend- 

 ing in so complete a manner as in the instance described by Meckel, 

 where the clavicular, acromial, and scapular fibres were all perfectly dis- 

 tinct and separate. 



6. The coraco-brachialis in a few instances (three or four) was par- 

 tially divisible into two distinct planes; and in one subject these were 

 perfectly differentiated and separated by the external cutaneous nerve. 

 Of the two laminae in this instance the superficial was inserted lower 

 down than usual, and arose from the tip of the coracoid process, uncon- 

 nected with the short head of the biceps ; the deeper portion was con- 

 nected intimately with that muscle. I would look upon this variety as 

 of very great interest in determining the homotypical relations of this 

 muscle, which, I think, we are justified in considering as the represen- 

 tative of the adductor mass in the hinder limb ; the upper or shorter part 

 may perhaps represent the adductor brevis, or more probably magnus, 

 while the longer and more superficial element is the evident homotype 

 of the adductor longus. This we learn — 1st, from its origin, the dimi- 

 nished homotype of the ischiatic element, and this in a situation where 

 the pubis is obsolete ; 2nd, from its relation to the brachial artery ; and, 

 3rd, from its insertion. Among the Mammals we find the coraco-bra- 

 chialis thus divided in the ornithorhynchus, lemur, bear, and others. 



7. The supinator longus and (8) psoas magnus were split into two 

 portions in one subject — the former by the radial nerve, the latter by the 

 anterior crural. 



