THE ANTERIOR BRACHIAL REGION. 



393 



The Flexor profundus digitorum 

 (perforans) (Fig. 234) is situated on 

 the ulnar side of the forearm, im- 

 icdiately beneath the superficial 

 flexors. It arises from the upper 

 three-fourths of the anterior and 

 inner surfaces of the shaft of the 

 ulna, embracing the insertion of the 

 Brachialis anticus above, and extend- 

 ing, 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 three- 

 fourths of the posterior border of the 

 ulna, in common with the Flexor and 

 Extensor carpi ulnaris; and from the 

 ulnar half of the interosseous mem- 

 brane. The fibres form a fleshy belly 

 of considerable size, which divides 

 into four tendons : these pass under 

 the annular ligament beneath the 

 tendons of the Flexor sublimis digi- 

 torum. Opposite the first phalanges 

 the tendons pass through the openings 

 in the tAvo slips of the tendons of the 

 Flexor sublimis digitorum, and are 

 finally inserted into the bases of the 

 last phalanges. The portion of the 

 muscle for the index finger is usually 

 distinct throughout, but the tendons 

 for the three inner fingers are con- 

 nected together by cellular tissue and 

 tendinous slips as far as the palm of 

 the hand. The tendons of this muscle 

 and those of the Flexor sublimis digi- 

 torum, whilst contained in the osseo- 

 aponeurotic canals of the fingers, are 

 invested in a synovial sheath, and are 

 connected to each other and to the 

 phalanges by slender tendinous fila- 

 ments, called vincula accessoria ten- 

 dinum. One of these connects the 

 deep tendon to the bone before it 

 passes through the superficial tendon ; 

 a second connects the two tendons 

 together, after the deep tendons have 

 passed through ; and a third connects 

 the deep tendon to the head of the 

 second phalanx. This last consists 

 largely of yellow elastic tissue, and 

 may assist in drawing down the ten- 

 don after flexion of the finger. 1 



Four small muscles, the Lurnbri- 

 cales, are connected with the tendons 

 of the Flexor profundus in the palm. 

 They will be described with the mus- 

 cles in that region. 



FIG. 234. Front of the left forearm. Deep muscles. 

 1 Marshall, Brit, and For. Med.-Chir. Rer., 1853. 



