186 OSTEOLOGY 
posterior limb of the Y winds obliquely round the outer side of the bone towards 
the posterior surface, 
GREAT 
‘ TUBEROSITY 
ANATOMICAL_£. 
NECK f[& 
™Teres minor 
SURGICAL NECK 
Triceps (outer head)— 
ARTERIAL _ 
FORAMEN 
—— Deltoid 
SPIRAL GROOVE 
Triceps (inner head) 
OLECRANON y: 
FOSSA 8a a 
Tendon of 
flexor muscles 
INTERNAL 
EPICONDYLE 
at) 
Y Anconeus 
GROOVE FOR — 
ULNAR NERVE 
TROCHLEA 
Fic. 129.—Postrrionk View OF THE RiGHT HUMERUS. 
Infraspinatus 
DELTOID EMINENCE 
Brachialis anticus 
EXTERNAL 
SPICONDYLE 
where it becomes continuous with a slightly elevated and 
occasionally rough ridge which leads 
up the back of the bone towards the 
great tuberosity superiorly; from 
this latter ridge the outer head of 
the triceps muscle arises. 
The inner surface of the shaft 
about its middle inclines to form 
a rounded border, on which there 
is often a rough linear impression, 
which marks the insertion of the 
coraco-brachialis muscle. Below 
this the shaft becomes compressed 
and expanded laterally, ending 
inferiorly on either side in the 
condyles. Its surfaces are now 
anteriorand posterior, being separated 
from each other by two clearly de- 
fined borders, the epicondylic ridges. 
Of these, the internal, margo 
medialis, is the more curved and less 
prominent, and is continuous above 
with the surface to which the coraco- 
brachialis is attached, whilst in- 
feriorly it ends by blending with 
the internal condyle. The external 
epicondy le ridge, margo lateralis, 
is straighter and more projecting ; 
its edge is usually distinctly lipped. 
Confluent with the external condyle 
inferiorly, it may be traced upwards 
to near the deltoid eminence, where 
it turns backwards more or less 
parallel to the posterior oblique 
border of that impression, to be lost 
on the posterior surface of the shaft. 
The interval between this border 
and the deltoid eminence is thus 
converted into a shallow oblique 
furrow, which winds round the outer 
surface of the bone just below its 
middle ; this constitutes the musculo- 
spiral groove (sulcus radialis) along 
which the. musculo-spiral nerve, to- 
gether with the superior profunda 
artery, passes from the back to reach 
the front of the arm. To the epi- 
condylic ridges are attached the 
intermuscular septa, whilst the ex- 
ternal in its upper two-thirds 
furnishes a surface for the origin 
of the brachio-radialis (supinator- 
longus), and in its lower third for 
the extensor carpi radialis longior 
muscle. 
The anterior surface of the lower 
half of the shaft is of elongated triangular form, the base corresponding to the 
inferior extremity of the bone. 
tunning down the centre of this is a broad, 
