HUMERUS. 131 



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

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

 bicipital groove, and gives attachment from above downwards to the tendons of 

 the Latissimus dorsi, Teres major, and part of the origin of the inner head of the 

 Triceps. About its centre is a rough ridge for the attachment of the Coraco- 

 brachialis, and just below this is seen the entrance of the nutritious canal directed 

 downwards. Sometimes there is a second canal higher up, which takes a similar 

 direction. Its inferior third is raised into a slight 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 aponeurosis. 



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

 and covered by the Deltoid muscle ; forwards below, where it is slightly concave 

 from above downwards, 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, forwards and downwards ; it transmits the musculo-spiral 

 nerve and superior profunda artery. 



The internal surface, less extensive than the external, is directed forwards 

 above, forwards and inwards below ; at its upper part it is narrow, and forms the 

 bicipital groove. The middle part of this surface is slightly rough for the 

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

 attachment to the Brachialis anticus muscle. 1 



The posterior surface (fig. 88) appears somewhat twisted, so that its upper part 

 is directed a little inwards, its lower part backwards, and a little outwards. 

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

 the Triceps, the former being attached to its upper and outer part, the latter to 

 its inner and back part, their origin being separated by the musculo-spiral groove. 



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

 forwards : it terminates below in a broad articular surface, which is divided into 

 two parts by a slight ridge. On either side of the articular surface are the ex- 

 ternal and internal condyles. The articular surface extends a little lower than 

 the condyles, and is curved slightly forwards, so as to occupy the more anterior 

 part of the bone ; its greatest breadth is in the transverse diameter, and it' is 

 obliquely directed, so that its inner extremity occupies a lower level than the 

 outer. The outer portion of the articular surface presents a smooth rounded 

 eminence, which has received the name of the lesser or radial head of the humerus ; 

 it articulates with the cup-shaped depression on the head of the radius, is limited 

 to the front and lower part of the bone, not extending as far back as the other 

 portion of the articular surface. On the inner side of this eminence is a shallow 

 groove, in which is received the inner margin of the head of the radius. The 

 inner or trochlear portion of the articular surface presents a deep depression 

 between two well-marked borders. This surface is convex from before back- 

 wards, concave from side to side, and occupies the anterior lower and posterior parts 

 of the bone. The external border, less prominent than the internal, corresponds 



1 A small hook-shaped process of bone, varying from T ' ff to f of an inch in length, is not 

 unfrequently found projecting from the inner surface of the shaft of the humerus two inches 

 above the internal condyle. It is curved downwards, forwards, and inwards, 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 interosseous 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 supra-condyloid 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. STKUTHERS, in his "Anatomical and Physiological Observations," p. 202. 



