250 THE SKELETON. 



upper part is very prominent and rough, and forms the outer lip of the bicipital 

 groove. It is here often called the external bicipital ridge, and serves for the 

 attachment of the tendon of the Pectoralis major. About its centre it forms the 

 anterior boundary of the rough deltoid impression ; below, it is smooth and rounded, 

 affording attachment to the Brachialis anticus. 



The external border runs from the back part of the greater tuberosity to the 

 external condyle, and separates the external from the posterior surface. It is 

 rounded and indistinctly marked in its upper half, serving for the attachment of 

 the lower part of the insertion of the Teres minor, and below this of the external 

 head of the Triceps muscle ; its centre is traversed by a broad but shallow, oblique 

 depression, the musculo-spiral groove ; its lower part is marked by a prominent, 

 rough margin, a little curved from behind forward, the external supracondylar 

 ridge, which presents an anterior lip for the attachment of the Supinator longus 

 above and Extensor carpi radialis longior below, a posterior lip for the Triceps, 

 and an interstice for the attachment of the external intermuscular septum. 



The internal border extends from the lesser tuberosity to the internal condyle. 

 Its upper third is marked by a prominent ridge, forming the internal lip of the 

 bicipital groove, and gives attachment to the tendon of the Teres major. About 

 its centre is a rough ridge for the attachment of the Coraco-brachialis, and just 

 below this is seen the entrance of the nutrient canal, directed downward. Some- 

 times there is a second canal higher up, which takes a similar direction. The infe- 

 rior third of this border is raised into a slight ridge, the internal supracondylar 

 ridge, which becomes very prominent below ; it presents an anterior lip for the 

 attachment of the Brachialis anticus, a posterior lip for the internal head of the 

 Triceps, and an intermediate space for the internal intermuscular septum. 



The external surface is directed outward above, where it is smooth, rounded, 

 and covered by the Deltoid muscle ; forward and outward below, where it is 

 slightly concave from above downward, and gives origin to part of the Brachialis 

 anticus muscle. About the middle of this surface is seen a rough, triangular 

 impression for the insertion of the Deltoid muscle ; and below it the musculo-spiral 

 groove, directed obliquely from behind, forward and downward, and transmitting 

 the musculo-spiral nerve and superior profunda artery. 



The internal surface, less extensive than the external, is directed inward above, 

 forward and inward below ; at its upper part it is narrow and forms the floor of 

 the bicipital groove : to it is attached the Latissimus dorsi. The middle part of 

 this surface is slightly rough for the attachment of some of the fibres of the tendon 

 of insertion of the Coraco-brachialis ; its lower part is smooth, concave, and gives 

 attachment to the Brachialis anticus muscle. 1 



The posterior surface (Fig. 198) appears somewhat twisted, so that its upper 

 part is directed a little inward, its lower part backward and a little outward. 

 Nearly the whole of this surface is covered by the external and internal heads of 

 the Triceps, the former of which is attached to its upper and outer part, the latter 

 to its inner and back part, the two being separated by the musculo-spiral groove. 



The Lower Extremity is flattened from before backward, and curved slightly 

 forward ; it terminates below in a broad, articular surface which is divided into 

 two parts by a slight ridge. Projecting on either side are the external and inter 



1 A small, hook-shaped process of bone, varying from -fa to of an inch in length, is not unfre- 

 quently found projecting from the inner surface of the shaft of the humerus two inches above the 

 internal condyle. It is curved downward, forward, and inward, and its pointed extremity is connected 

 to the internal border, just above the inner condyle, by a ligament or fibrous band, completing an 

 arch through which the median nerve and brachial artery pass when these structures deviate from 

 their usual course. Sometimes the nerve alone is transmitted through it, or the nerve may be 

 accompanied by the ulnar artery in cases of high division of the brachial. A well-marked 

 groove is usually found behind the process in which the nerve and artery are lodged. This 

 space is analogous to the supracondyloid foramen in many animals, and probably serves 

 in them to protect the nerve and artery from compression during the contraction of the 

 muscles in this region. A detailed account of this process is given by Dr. Struthers, in 

 his Anatomical and Physiological Observations, p. 202. An accessory portion of the Coraco- 

 brachialis muscle is frequently connected with this process, according to Mr. J. Wood, (Journal of Anat. 

 (ina Phys., No. 1, Nov., 1866, 'p. 47). 



