392 THE MUSCLES AND FASCIAE. 



to it and the Extensor carpi ulnaris and Flexor profundus digitorum ; and from 

 the intermuscular septum between it and the Flexor sublimis digitorum. The 

 fibres terminate in a tendon which occupies the anterior part of the lower half of 

 the muscle, and is inserted into the pisiform bone, and is prolonged from this to- 

 the fifth metacarpal and unciform bones, by the piso-metacarpal and piso-uncinate 

 lio-aments : it is also attached by a few fibres to the annular ligament. The ulnar 

 artery lies on the outer side of the tendon of this muscle, in the lower two-thirds of 

 the forearm, the tendon forming a guide in tying the vessel in this situation. 



Relations. By its superficial surface, with the deep fascia, with which it is 

 intimately connected for a considerable extent ; by its deep surface, with the Flexor 

 sublimis digitorum, the Flexor profundus digitorum, the Pronator quadratus, and 

 the ulnar vessels and nerve; by its outer or radial border, with the Palmaris 

 longus above and the ulnar vessels and nerve below. 



The Flexor sublimis digitorum (perforatus) is placed beneath the preceding 

 muscles, which therefore must be removed in order to bring its attachment into 

 view. It is the largest of the muscles of the superficial layer, and arises by three 

 heads. One head arises from the internal condyle of the humerus by the common 

 tendon, from the internal lateral ligament of the elbow-joint, and from the inter- 

 muscular septum common to it and the preceding muscles. The second head arises 

 from the inner side of the coronoid process of the ulna, above the ulnar origin of 

 the Pronator radii teres (Fig. 100, p. 151). The third head arises from the oblique 

 line of the radius, extending from the tubercle to the insertion of the Pronator 

 radii teres. The fibres pass vertically downward, forming a broad and thick muscle, 

 which speedily divides into two planes of muscular fibres, superficial and deep : the 

 superficial plane divides into two parts which end in tendons for the middle and 

 ring fingers ; the deep plane also divides into two parts, which end in tendons for 

 the index and little fingers, but previously to having done so, it gives off a mus- 

 cular slip, which joins that part of the superficial plane which is intended for the 

 ring finger. As the four tendons thus formed pass beneath the annular ligament 

 into the palm of the hand, they are arranged in pairs, the superficial pair corres- 

 ponding to the middle and ring fingers, the deep pair to the index and little fingers. 

 The tendons diverge from one another as they pass onward. Opposite the bases of 

 the first phalanges each tendon divides into two slips, to allow of the passage of 

 the corresponding tendon of the Flexor profundus digitorum ; the two portions of 

 the tendon then unite and form a grooved channel for the reception of the accom- 

 panying deep flexor tendon. Finally they subdivide a second time, to be inserted 

 into the sides of the second phalanges about their middle. After leaving the palm, 

 these tendons, accompanied by the deep flexor tendons, lie in osseo-aponeurotic 

 canals (Fig. 234). These canals are formed by strong fibrous bands, which arch 

 across the tendons, and are attached on each side to the margins of the phalanges. 

 Opposite the middle of the proximal and second phalanges the sheath is very 

 strong, and the fibres pass transversely ; but opposite the joints it is much thinner, 

 and the fibres pass obliquely. Each sheath is lined by a syiiovial membrane, 

 which is reflected on the contained tendons. 



Relations. In the forearm, by its superficial surface, with the deep fascia and 

 all the preceding superficial muscles ; by its deep surface, with the Flexor profundus 

 digitorum, Flexor longus pollicis, the ulnar vessels and nerve, and the median 

 nerve. In the hand its tendons are in relation, in front, with the palmar fascia, 

 superficial palmar arch, and the branches of the median nerve ; behind, with the 

 tendons of the deep Flexor and the Lumbricales. 



Deep Layer. 



Flexor profundus digitorum. Flexor longus pollicis. 



Pronator quadratus. 



Dissection. Divide each of the superficial muscles at its centre, and turn either end aside; 

 the deep layer of muscles, together with the median nerve and ulnar vessels, will then be 

 exposed. 



