390 THE MUSCLES AND FASCIA. 



The deep fascia of the forearm, continuous above with that enclosing the arm, 

 is a dense, highly glistening aponeurotic investment, which forms a general sheath 

 enclosing the muscles in this region ; it is attached, behind, to the olecranon and 

 posterior border of the ulna, and gives off' from its inner surface numerous inter- 

 muscular septa, which enclose each muscle separately. Below, it is continuous in 

 front with the anterior annular ligament, and forms a sheath for the tendon of the 

 Palmaris longus muscle, which passes over the annular ligament to be inserted 

 into the palmar fascia. Behind, near the wrist-joint, it becomes much thickened 

 by the addition of many transverse fibres, and forms the posterior annular liga- 

 ment. It consists of circular and oblique fibres, connected together by numerous 

 vertical fibres. It is much thicker on the dorsal than on the palmar surface, and 

 at the lower than at the upper part of the forearm, and is strengthened above by 

 tendinous fibres derived from the Brachialis anticus and Biceps in front, and from 

 the Triceps behind. Its deep surface gives origin to muscular fibres, especially 

 at the upper part of the inner and outer sides of the forearm, and forms the 

 boundaries of a series of conical-shaped cavities, in which the muscles are 

 contained. Besides the vertical septa separating each muscle, transverse septa are 

 given off both on the anterior and posterior surfaces of the forearm, separating the 

 deep from the superficial layer of muscles. Numerous apertures exist in the fascia 

 for the passage of vessels and nerves ; one of these, of large size, situated at the 

 front of the elbow, serves for the passage of a communicating branch between the 

 superficial and deep veins. 



The muscles of the forearm may be subdivided into groups corresponding to 

 the region they occupy. One group occupies the inner and anterior aspect of the 

 forearm, and comprises the Flexor and Pronator muscles. Another group occupies 

 its outer side, and a third its posterior aspect. The two latter groups include all 

 the Extensor and Supinator muscles. 



8. Anterior Radio -ulnar Region. 



The muscles in this region are divided for convenience of description into two 

 groups or layers, superficial and deep. 



Superficial Layer. 



Pronator radii teres. Flexor carpi ulnaris. 



Flexor carpi radialis. Flexor sublimis digitorum. 



Palmaris longus. 



These muscles take origin from the internal condyle of the humerus by a 

 common tendon. 



The Pronator radii teres arises by two heads. One, the larger and more 

 superficial, arises from the humerus, immediately above the internal condyle, and 

 from the tendon common to the origin of the other muscles ; also from the fascia 

 of the forearm and intermuscular septum between it and the Flexor carpi radialis. 

 The other head is a thin fasciculus which arises from the inner side of the 

 coronoid process of the ulna, joining the preceding at an acute angle. Between 

 the two heads the median nerve enters the forearm. The muscle passes obliquely 

 across the forearm from the inner to the outer side, and terminates in a flat tendon, 

 which turns over the outer margin of the radius, and is inserted into a rough im- 

 pression at the middle of the outer surface of the shaft of that bone. 



Relations. By its anterior surface, throughout the greater part of its extent, 

 with the deep fascia ; at its insertion it is crossed by the radial vessels and nerve, 

 and covered by the Supinator longus ; by its posterior surface, with the Brachialis 

 anticus, Flexor sublimis digitorum, the median nerve, and ulnar artery, the small 

 or deep head being interposed between the two latter structures. Its outer border 

 forms the inner boundary of a triangular space in which are placed the brachial 

 artery, median nerve, and tendon of the Biceps muscle. Its inner border is in 

 contact with the Flexor carpi radialis. 



