308 MUSCLES AND FASCIAE. 



and little fingers. The tendons diverge from one another as they pass onwards, 

 and are finally inserted into the lateral margins of the second phalanges, about 

 their centre. Opposite the base of the first phalanges, each tendon divides, so as 

 to leave a fissured interval, between which passes one of the tendons of the Flexor 

 profundus, and they both enter an osseo-aponeurotic canal, formed by a strong 

 fibrous band which arches across them, and is attached on each side to the margins 

 of the phalanges. The two portions into which the tendon of the Flexor sublimis 

 divides, so as to admit of the passage of the deep flexor, expand somewhat, and 

 form a grooved channel, into which the accompanying deep flexor tendon is 

 received ; the two divisions then unite, and finally subdivide a second time to be 

 inserted into the fore part and sides of the second phalanges. The tendons, whilst 

 contained in the fibro-osseous canals, are connected to the phalanges by slender 

 tendinous filaments, called vincula accessoria tendinum. A sy no vial sheath invests 

 the tendons as they pass beneath the annular ligament ; a prolongation from which 

 surrounds each tendon as it passes along the phalanges. 



Relations. In the Forearm. By its anterior surface, with the deep fascia and 

 all the preceding superficial muscles. By its posterior 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. 



ANTERIOR BRACHIAL EEGION. 



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; 



The Flexor Profundus Digitorum (perforans) is situated on the ulnar side of the 

 forearm, immediately beneath the superficial Flexors. It arises from the upper 

 two-thirds of the anterior and inner surfaces of the shaft of the ulna, embracing, 

 above, the insertion of the Brachialis anticus, and extending, below, to within a 

 short distance of the Pronator quadratus. It also arises from a depression on the 

 inner side of the coronoid process, by an aponeurosis from the upper two-thirds 

 of the posterior border of the ulna, and from the ulnar half of the interosseous 

 membrane. The fibres form a fleshy belly of considerable size, which divides 

 into four tendons, which pass under the annular ligament beneath the tendons 

 of the Flexor sublimis. Opposite the first phalanges, the tendons pass between 

 the two slips of the tendons of the Flexor sublimis, and are finally inserted into 

 the bases of the last phalanges. The tendon of the index finger is distinct ; the 

 rest are connected together by cellular tissue and tendinous slips, as far as the 

 palm of the hand. 



Four small muscles,* the Lumbricales, are connected with the tendons of the 

 Flexor profundus in the palm. They will be described with the muscles in that 

 region. 



delations. By its anterior surface, in the forearm, with the Flexor sublimis 

 digitorum, the Flexor carpi ulnaris, the ulnar vessels and nerve, and the median 

 nerve; and in the hand, with the tendons of the superficial Flexor. By its 

 posterior surface, in the forearm, with the ulna, the interosseous membrane, the 

 Pronator quadratus ; and in the hand, with the Interossei, Adductor pollicis, and 

 deep palmar arch. By its ulnar border, with the Flexor carpi ulnaris. By its 

 radial border, with the Flexor longus pollicis, the anterior interosseous vessels and 

 nerve being interposed. 



