52 ANATOMY IN A NUTSHELL. 



the external, or long humeral; and (3) the internal, or short humeral head. 

 The common tendon of the Triceps commences about the middle of the back 

 part of the muscle; it consists of two aponeurotic lamina', one of which is sub- 

 cutaneous and covers the posterior surface of the muscle for the lower half of 

 it- extenl : the other is more deeply seated in the substance of the muscle. After 

 receiving the attachment of the muscular fibers they join together above the 

 elbow, forming the tendon of Insertion. A small bursa is situated beneath the 

 tendon. 



Origin.- The middle or long head arises from a rough triangular depres- 

 sion on the scapula, just below the glenoid cavity, being blended at its upper 

 part with the capsular ligament. (Plate XXI.) 



The external head arises from the posterior surface of the shaft of humerus, 

 between the insertion of the Teres minor and the upper pari of the musculo- 

 spiral groove; also from the external border of the humerus and external in- 

 termuscular septum. (Plate XXII.) 



The internal head arises from the posterior surface of shaft of humerus, 

 below the groove for the musculo-spiral nerve, extending from the insertionof 

 the Teres major to within an inch of the trochlear surface; also from the internal 

 borderof the humerus andfrom the back of the whole length ofthe internal and 

 lower part of the external intermuscular septum. (Plate XXII.) 



Insertion.- Upper end of olecranon process of ulna, a band of fibers being 

 continued downward to blend with the deep fascia of forearm. (Plate XXIV.) 



Action- Extensor of forearm. 



Nerve Supply- Seventh and eighth cervical through musculo-spiral. 



Blood Si pply — Brachial and superior profunda. 



Latissimus dorsi. — Description. — (Plate XYIII.) — This is a broad, flat 

 muscle which rovers the lumbar and lower half of the dorsal regions and is 

 gradually contracted into a narrow fasciculus which passes upward across the 

 interior angle of the scapula, and occasionally receives a few fibers from it. It 

 belongs to the first layer of muscles in the back. 



The muscle then curves around the lower border of the Teres major, and is 

 twisted upon itself. It terminates in a short, quadrilateral tendon, about three 

 inches in length, which, as it passes in front of the tendon of the Teres major 

 becomes united with it. the surfaces of the two being separated by a bursa; 

 another bursa is sometimes interposed between the muscle and the inferior 

 angle of the scapula. At the insertion of this muscle an expansion is given off 

 to the deep fascia of the arm. There IS usually a fibrous slip which passes from 

 the lower border of the tendon of the Latissimus dorsi. near its insertion, to the 

 long head of die Triceps. This is occasionally muscular and is the representa- 

 tive of the Dorso-epitrochlearis muscle of apes. 



Origin. From the spinous processes of die six inferior dorsal vertebra?, 

 and from the posterior layer of the lumbar fascia, by which it is attached to the 

 spines of die lumbar ami sacral vertebrae, and to the supraspinous ligament, 

 also from the external lip of the cresl of the ilium behind theorigin of the ex- 

 ternal oblique, and bv fleshy digitations from the three or four lower ribs, which 



