MORPHOLOGY OF THE LIMB-MUSCLES. 275 



which corresponds to the latissimus dorsi and teres major, with probably the hinder part of 

 the deltoid. 



All the other muscles of the limb are intrinsic, and in their relation to the several 

 segments are arranged in groups which may in the main be compared homologically with 

 each other. These groups also show a primary division into dorsal or extensor masses, 

 supplied by the posterior branches of the limb-nerves, and ventral or flexor masses, receiving 

 their nerves generally from, the anterior branches of the trunks entering the limbs. 1 The 

 manner in which these masses are cleft to form separate muscles, however, is found to vary- 

 in the two limbs, especially in their proximal portions, in accordance with difference of 

 function, and thus a precise correspondence between individual muscles is not always to be 

 looked for. In the distal segments of both limbs the muscles, although more numerous, 

 become shorter and more uniform in their disposition, and hence the hombldgy becomes 

 more apparent between the muscles of the hand and foot than in those situated nearer the 

 roots of the limbs. 



The intrinsic muscles passing from the girdle to the first segment of the limb have been 

 partly referred to above, in so far as they are closely connected with extrinsic muscles passing 

 from the trunk, and where extrinsic muscles of the upper limb are represented by intrinsic 

 muscles of the lower limb (e.g. pectoralis major and the superficial adductors). The dorsal 

 muscles are respectively scapulo-humeral and ilio-femoral ; the ventral fall into claviculo- 

 humeral (part of the pectoralis major) and pubo-femoral (adductors longus and brevis), and 

 coraco-humeral and ischio-femoral. In accordance with the homologies that have been traced 

 between the different parts of the scapula and ilium (p. 141), the subscapularis is represented 

 by the gluteus medius and minimus, and the infraspinatus by the iliacus, while there appears 

 to be no separate muscle at the hip corresponding to the supraspinatus of the shoulder. The 

 teres minor is probably a derivative of the hinder part of the deltoid, the connection between 

 the two being indicated occasionally by slips joining the latter muscle from the lower part of 

 the scapula ; the pyrif ormis is a segmentation of the same mass as the two smaller glutei : 

 and the pectineus appears from its innervation to be a displaced part of the iliacus : these 

 muscles have no separate representatives in the other limb. The coraco-humeral muscles 

 in man and mammals generally are much reduced in comparison with their condition in the 

 lower vertebrate forms, where the coracoid element of the shoulder-girdle is of large 

 size, their function as adductors being discharged by muscles passing from the trunk : they 

 form the several parts of the coraco-brachialis muscle (p. 219). The ischio-femoral muscles, 

 on the other hand, are largely developed, and give rise to the quadratus femoris and adductor 

 magnus, together with the obturators and gemelli : the obturator internus has extended its 

 origin from the ischium to the inner surface of the pelvis, and the gemelli are portions of the 

 muscle retaining the original connection. The adductor magnus probably contains also, in 

 the part supplied by the great sciatic nerve, an element derived from the long flexor mass of 

 the thigh, and the attachment to the tibia represented by the internal lateral ligament of the 

 knee (p. 184) may be the insertion of this element. 



In the first segment of the limb the flexor and extensor masses both show a division into a 

 superficial long part arising from the limb-girdle, and a deep short part springing from the 

 bone of the segment ; but considerable differences exist in the mode of cleavage of these parts 

 and in the insertion of the muscles thus formed. The sartorius is a derivative of the long 

 extensor of the thigh, and may be compared to the dorso-epitrochlearis of the arm. 



In the middle segment also a similar division into superficial long muscles arising from the 

 bone of the upper segment, and short deep muscles arising from the bones of the proper 

 segment, is to be recognized. These muscles are for the most part inserted into the distal 

 segment of the limb, passing either to the metacarpal (or metatarsal) bones or to the digital 

 phalanges, but in the forearm the pronators and supinators become separated off from the 

 flexors and extensors respectively, and are inserted into the radius. In the leg in man there is 

 only one such muscle developed, viz., the popliteus, corresponding to the pronator teres of the 

 forearm. In comparing the musculature of the leg with that of the forearm marked 

 differences are observed, which may for the most part be referred to the following heads : 1, 

 a reduction in number in accordance with the diminution of mobility, and due partly to less 

 complete differentiation and partly to suppression or absence of certain elements ; 2, the dis- 

 appearance of the high origin of some of the superficial muscles, especially those of the 

 extensor group ; and 3, the development of insertions into the tarsal bones, most conspicuous 

 in the case of the superficial flexors which, owing to the outgrowth of the heel, become 

 completely separated from their continuations in the foot. In the arrangement of the deep 

 extensor muscles, which in the upper limb arise from the forearm bones, whereas in the lower 



1 The only exceptions to this statement as to the nervous supply of the muscular groups are the 

 short head of the biceps in the lower limb, which is supplied from the external popliteal division of the 

 great sciatic nerve the posterior or extensor nerve of the distal portion of the limb, and the brachialis 

 anticus, which commonly receives a small branch from the musculo-spiral the extensor nerve-trunk of 

 the upper limb. 



