THE VOLAR ANTIBRACHIAL MUSCLES 44J 



digitorum sublimis. Opposite the first phalanges the tendons pass through the 

 openings in the tendons of the Flexor digitorum sublimis, 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 middle, ring, and little 

 fingers are connected together by areolar tissue and tendinous slips, as far as the 

 palm of the hand. 



Fibrous Sheaths of the Flexor Tendons. After leaving the palm, the tendons 

 of the Flexores digitorum sublimis and profundus lie in osseo-aponeurotic canals 

 (Fig. 427), formed behind by the phalanges and in front by strong fibrous bands, 

 which arch across the tendons, and are attached on either side to the margins of 

 the phalanges. Opposite the middle of the proximal and second phalanges the 

 bands (digital vaginal ligaments) are very strong, and the fibers are transverse; 

 but opposite the joints they are much thinner, and consist of annular and cruciate 

 ligamentous fibers. Each canal contains a mucous sheath, which is reflected on 

 the contained tendons. 



Within each canal the tendons of the Flexores digitorum sublimis and profundus 

 are connected to each other, and to the phalanges, by slender, tendinous bands, 

 called vincula tendina (Fig. 416). There are two sets of these; (a) the vincula 

 brevia, which are tw r o in number in each finger, and consist of triangular bands 

 of fibers, one connecting the tendon of the Flexor digitorum sublimis to the front 

 of the first interphalangeal joint and head of the first phalanx, and the other the 

 tendon of the Flexor digitorum profundus to the front of the second interphalan- 

 geal joint and head of the second phalanx; (6) the vincula longa, which connect 

 the under surfaces of the tendons of the Flexor digitorum profundus to thos j of the 

 subjacent Flexor sublimis after the tendons of the former have passed through 

 the latter. 



Variations. The index finger portion may arise partly from the upper part of the radius. Slips 

 from the inner head of the Flexor sublimis, medial epicondyle, or the coronoid are found. Connec- 

 tion with the Flexor pollicis longus. 



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

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

 hand (page 464). 



The Flexor pollicis longus is situated on the radial side of the forearm, lying 

 in the same plane as the preceding. It arises from the grooved volar surface of 

 the body of the radius, extending from immediately below the tuberosity and 

 oblique line to within a short distance of the Pronator quadratus. It arises also 

 from the adjacent part of the interosseous membrane, and generally by a fleshy 

 slip from the medial border of the coronoid process, or from the medial epicondyle 

 of the humerus. The fibers end in a flattened tendon, which passes beneath the 

 transverse carpal ligament, is then lodged between the lateral head of the Flexor 

 pollicis brevis and the oblique part of the Adductor pollicis, and, entering an osseo- 

 aponeurotic canal similar to those for the Flexor tendons of the fingers, is inserted 

 into the base of the distal phalanx of the thumb. The volar interosseous nerve 

 and vessels pass downward on the front of the interosseous membrane between 

 the Flexor pollicis longus and Flexor digitorum profundus. 



Variations. Slips may connect with Flexor sublimis, or Profundus, or Pronator teres. An addi- 

 tional tendon to the index finger is sometimes found. 



The Pronator quadratus is a small, flat, quadrilateral muscle, extending across 

 the front of the lower parts of the radius and ulna. It arises from the pronator 

 ridge on the lower part of the volar surface of the body of the ulna; from the medial 

 part of the volar surface of the lower fourth of the ulna; and from a strong apon- 

 eurosis which covers the medial third of the muscle. The fibers pass lateral ward 

 29 



