THE HUMERUU, OR ARM BONE 



181 



below; it presents an anterior lip for the 

 attachment of the Brachialis anticus muscle, 

 a posterior lip for the internal head of the 

 Triceps muscle, and an intermediate spave 

 for the attachment of the internal intermus- 

 cular septum. 



The external surface (fades anterior later- 

 alis] is directed outward above, where it is 

 smooth, rounded, and covered by the Del- 

 toid 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 mid- 

 dle of this surface is seen a rough, trian- 

 gular impression for the insertion of the 

 Deltoid muscle, deltoid impression, and be- 

 low this the musculospiral groove, directed 

 obliquely from behind forward and down- 

 ward, and transmitting the musculospiral 

 nerve and superior profunda artery. 



The internal surface (Jades anterior medi- 

 alis}, 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 

 roughened for the attachment of some of 

 the fibres of the tendon of insertion of the 

 Coracobrachialis; its lower part is smooth, 

 concave from above downward, and gives 

 attachment to the Brachialis anticus mus- 

 cle. 1 A little below the middle of the shaft 

 is the nutrient foramen. This leads into a 

 nutrient canal, which is directed toward the 

 elbow-joint. 



The posterior surface (fades posterior} 

 (Fig. 142) 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 

 bv the external and internal heads of the 



1 A small hook-shaped process of bone, the suprricoiidulnr 

 process, varying from VJQ to 3 /4of an inch in length, is not in- 

 frequently 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, 

 which gives origin to a portion of the Pronator teres; through 

 the arch completed by this fibrous band 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 anal- 

 ogous 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. 



_Capstdar 

 ligament 



Capsvlar 

 ligament 



Jro ch Lt 



FIG. 142. Left humerus. Posterior surface. 



