THE FOREARM. 479 



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 by 

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

 the Triceps behind. Its inner 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. 



Anterior Radio -Ulnar Region. 



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 passes the median nerve. 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 impression 

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



Relations. By its anterior surface, with the deep fascia, the Supinator longus, 

 and the radial vessels and nerve ; 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 (cubital fossa) in which is placed 

 the brachial artery, median nerve, and tendon of the Biceps muscle. Its inner 

 border is in contact with the Flexor carpi radialis. 



Surgical Anatomy. This muscle, when suddenly brought into very active use, as in the 

 game of lawn tennis, is apt to be strained, producing slight swelling, tenderness, and pain on 

 putting the muscle into action. This is known as "lawn-tennis arm." 



The Flexor carpi radialis lies on the inner side of the preceding muscle. It 

 arises from the internal condyle by the common tendon, from the fascia of the fore- 

 arm, and from the intermuscular septa between it and the Pronator radii teres, on 

 the outside, the Palmaris longus internally, and the Flexor sublimis digitorum 

 beneath. Slender and aponeurotic in structure at its commencement, it increases 

 in size, and terminates in a tendon which forms the lower two-thirds of its length. 

 This tendon passes through a canal on the outer side of the annular ligament, 

 runs through a groove in the os trapezium (which is converted into a canal by a 

 fibrous sheath, and lined by a synovial membrane), and is inserted into the base 



