472 THE MUSCLES AND FASCIA 



scapulae vessels; it is bounded by the Teres minor above, the Teres major below, and the scapular 

 head of the Triceps externally; the quadrangular space transmits the posterior circumflex 

 vessels and the circumflex nerve; it is bounded by the Teres minor above, the Teres major 

 below, the scapular head of the Triceps internally, and the humerus externally. 



The Subanconeus is a name given to a few fibres from the under surface of 

 the lower part of the Triceps muscle, which are inserted into the posterior ligament 

 of the elbow-joint. By some authors it is regarded as the homotype of the 

 Subcrureus in the lower limb, but it is not a separate muscle. 



Nerves. The Triceps is supplied by the seventh and eighth cervical nerves through the 

 musculospiral nerve. 



Actions. The Triceps is the great Extensor muscle of the forearm, serving, when the forearm 

 is flexed, to extend the elbow-joint. It is the direct antagonist of the Biceps and Brachialis 

 anticus. When the arm is extended the Iqng head of the muscles may assist the Teres major 

 and Latissimus dorsi in drawing the humerus backward and in adducting it to the thorax. The 

 long head of the Triceps protects the under part of the shoulder-joint, and prevents displacement 

 of the head of the humerus downward and backward. The Subanconeus draws up the synovial 

 membrane of the elbow-joint out of the way of the advancing olecranon process during exten- 

 sion of the forearm. 



Applied Anatomy. The existence of the band of fibres from the Triceps to the fascia of the 

 forearm is of importance in excision of the elbow, and should always be carefully preserved 

 from injury by the operator, as by means of these fibres the patient is enabled to extend the 

 forearm, a movement which would otherwise mainly be accomplished by gravity that is to 

 say, allowing the forearm to drop from its own weight. 



III. MUSCLES AND FASCIA OF THE FOREARM. 



Dissection. To dissect the forearm, place the limb in the position indicated in Fig. 346, 

 make a vertical incision along the middle line from the elbow to the wrist, and a transverse 

 incision at the extremity of this; the superficial structures being removed, the deep fascia of 

 the forearm is exposed. 



The deep fascia of the forearm (fascia antibrachii)* 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 intermuscular 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 ligament. It consists of circular and oblique fibres, con- 

 nected 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 

 muscle 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 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. This fascia is also perforated 

 on its anterior surface, near the wrist, by the ulnar artery and nerve. 



1 The correct spelling is antebrachium, not antibrachium, as is given in the list of the BNA. [EDITOR.] 



