, 



THE HUMEKUS. 



207 



TERES MINOR 



INFRASPINATUS 



TRICEPS (lateral 

 head) 



DELTOID . 



BRACHIALIS 



GROOVE FOR 

 RADIAL NERVE 



The tuberositas deltoidea (deltoid tuberosity), to which the powerful deltoid muscle 

 is attached, is a rough, slightly elevated V-shaped surface, placed on the lateral 

 anterior surface of the body about its middle. The anterior limb of the V is 

 parallel to the axis of the body, and is continuous proximally with the lateral lip of 

 the intertubercular groove, whilst the posterior limb of the V winds obliquely 

 round the lateral anterior surface of the bone towards the posterior surface, where 

 it becomes continuous with a slightly elevated and 

 occasionally rough ridge which leads proximally 

 along the posterior aspect of the bone towards the 

 greater tubercle ; from this latter ridge the lateral 

 head of the triceps muscle arises. 



The medial anterior surface of the body about 

 its middle inclines to form a rounded border, on 

 which there is often a rough linear impression mark- 

 ing the insertion of the coracobrachialis muscle. 

 Distal to this the body becomes compressed from 

 before backwards and expanded from side to side, 

 ending dis tally on each side in an epicondyle. 

 Its surfaces are now anterior and posterior, being 

 separated from each other by two clearly denned 

 borders, the medial and lateral margins, or epi- 

 condylic ridges. Of these, the medial is the more 

 curved and less prominent, and is continuous proxi- 

 mally with the surface to which the coracobrachialis 

 is attached, whilst distally it ends by blending with 

 the medial epicondyle. The lateral is straighter 

 and more projecting ; its edge is usually distinctly 

 lipped. Confluent with the lateral epicondyle dis- 

 tally, it may be traced proximally to near the deltoid 

 tuberosity, where it turns backwards more or less 

 parallel to the posterior oblique border of that im- 

 pression, to be lost on the posterior surface of the 

 body. The interval between this border and the 

 deltoid eminence is thus converted into a shallow 

 oblique furrow, which winds round the lateral 

 surface of the bone just distal to its middle ; 

 this constitutes the groove for the radial nerve 

 along which the radial (O.T. musculo - spinal) 

 nerve, together with the profunda brachii artery, 

 passes from the back to reach the front of the arm. 

 To the epicondylic ridges are attached the inter- 

 muscular septa, whilst the lateral in its proximal 

 two-thirds furnishes a surface for the origin of the 

 brachioradialis muscle, and in its distal third for 

 the extensor carpi radialis longus muscle. 



The anterior surface of the distal half of the 

 body is of elongated triangular form, the base corre- 

 sponding to the distal extremity of the bone. Eunning down the centre of this is 

 a broad, rounded, elevated ridge, most pronounced proximally, where it joins the 

 deltoid tuberosity, and sloping on either side towards the epicondylic ridges ; it is 

 into the lateral of these slopes that the groove for the radial nerve passes. Distally 

 the elevated surface spreads out, and becomes confluent with the epicondyles. The 

 epicondylus medialis (medial epicondyle) is the more prominent of the two, and 

 furnishes a surface for the origin of the pronator teres, and the superficial flexor 

 muscles of the forearm. The epicondylus lateralis (lateral epicondyle), stunted and 

 but little projecting, serves for the attachment of the common tendon of origin of 

 the extensor' muscles. The brachialis muscle has an extensive origin from the 

 anterior surface of the distal half of the body, including between its proximal slips 

 the insertion of the deltoid. 



MEDIAL HEAD OF 



TRICEPS 



ORIGIN OF 

 EXTENSORS 



OF FOREARM 



ANCON^US 



FIG. 197. POSTERIOR SURFACE OF THE 

 EIGHT HUMERUS WITH ATTACHMENTS 

 OF MUSCLES MAPPED OUT. 



