476 



THE MUSCLES AND FASCIA 



unciform and pisometacarpal ligaments; it is also attached by a few fibres to 

 the annular ligament. 



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

 nected 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 (m. flexor digitorum sublimis} (Fig. 356) 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 super- 

 ficial layer, and arises by three heads. One head (caput humerale) arises from 

 the internal condyle of the humerus by the common tendon, from the internal 

 lateral ligament of the elbow-joint, and from the intermuscular septum common 

 to it and the preceding muscles. The second head (caput ulnare) arises from 

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

 Pronator teres (Fig. 145, p. 186). The third head (caput radiale) arises from the 

 oblique line of the radius, extending from the tuberosity to the insertion of the 

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

 muscle, which speedily divides into two planes of muscle 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 muscular 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 corresponding 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 

 (chiasma tendinum) to permit 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 accompanying deep Flexor tendon. 

 Finally, they subdivide a second time, to 

 be inserted into the sides of the second 

 phalanges about their middle. The inser- 

 tion in the index finger is shown in Fig. 

 363. After leaving the palm the tendons 

 of the superficial Flexor, accompanied 

 by the deep Flexor tendons, lie in osseo- 

 aponeurotic canals (Fig. 358). Each 

 canal or theca extends from the metacar- 

 pophalangeal articulation to the proxi- 

 mal end of the distal phalanx (Fig. 257). 

 It is 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. It is very thin over the metacarpo- 

 phalangeal articulation, and is absent over the distal phalanx. Each sheath 

 is lined by a synovia! membrane, which is reflected on the contained tendons. 



SHEATH OF. 

 FLEXOR' 



TENDONS 



FLEXOR PROFUNDUS 



DIGITORUM 



/FLEXOR 

 SUBLIMIS 

 DIGITORUM 

 DIGITAL 



ARTERIES 

 AND NERVES 



COMMON TENDON OF 

 'EXTENSOR MUSCLE 

 OF FINGERS 



FIRST PHALANX 



FIG. 357. Section passing through the middle 

 third of the first phalanx of the middle finger (frozen 

 section). The tendon of the Flexor sublimis digi- 

 torum is divided into two small bands, which spread 

 laterally and engage themselves between the osse- 

 ous plane and the Flexor profundus digitorum. 

 (Poirier and Charpy.) 



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

 ceding superficial muscles; by its deep surface, with the Flexor profundus digitorum, Flexor 



