THE HUMERUS. 
187 
rounded, elevated ridge, most pronounced above, where it joins the deltoid 
eminence, and sloping on either side towards the epicondylic ridges; it is into the 
outer of these slopes that the 
musculo- spiral groove — flows. 
Inferiorly the elevated surface 
spreads out, and becomes con- 
fluent with the condyles, more 
correctly termed the epicondyles. 
The internal epicondyle (epicon- 
dylus medialis) is the more 
prominent of the two, and 
furnishes a surface for the origin 
of the pronator radii teres, and 
the superficial flexor muscles of 
the forearm. The external epi- 
condyle (epicondylus lateralis), 
stunted and but little projecting, 
serves for the 
TROCHLEA 
CAPITELLUM 
Ext. EPICONDYLE 
OLECRANON FOSSA 
attachment of the 
Groove for ulnar nerve 
INT. EPI- £ 
CONDYLE 
LESSER TUBEROSITY 
Subseapularis 
}) /BICIPITAL GROOVE 
HEAD / 
Supra- 
spinatus 
GREAT 
TUBEROSITY 
EXT. Epr- 
: 
“ CONDYLE 
z 
Infra- 
spinatus 
Fig. 130.—THE HEAD OF THE RIGHT HUMERUS AS SEEN FROM 
ABOVE (with the outline of the lower extremity in relation 
thereto shown in dotted line. ) 
INT. EPICONDYLE 
Fic. 131.—THE LOWER EXTREMITY OF THE 
RicgHt HUMERUS AS SEEN FROM BELOW. 
common tendon of origin of the extensor 
muscles. The brachialis anticus muscle 
has an extensive origin from the anterior 
surface of the lower half of the shaft, in- 
cluding between its upper slips the inser- 
tion of the deltoid. 
The posterior surface of the lower half 
of the shaft is smooth and rounded from 
side to side; somewhat flattened below, 
where the whole shaft tends to incline 
forwards, it becomes continuous on either 
side with the posterior surfaces of the 
epicondyles, the inner of which is grooved 
for the passage of the ulnar nerve, whilst the external supplies an origin 
anconeus muscle. The inner head of the triceps 
muscle has an extensive origin from the posterior 
surface of the lower two-thirds of the shaft, internal 
to and below the musculo-spiral groove. 
The lower extremity of the humerus is furnished 
with two articular surfaces (the condyles proper), 
the outer of which, called the capitellum (capitu- 
lum), for articulation with the upper surface of the 
head of the radius, is a rounded eminence, placed 
on the anterior surface and lower border, but not 
extending upwards on the posterior surface of the 
inferior end of the bone. Above it, in front, there 
is a shallow depression (fossa radialis), into which 
the margin of the head of the radius sinks when the 
elbow is strongly flexed. A shallow groove separates 
the capitellum internally from the trochlea, which is 
a grooved articular surface, with prominent edges 
winding spirally round the lower extremity of the 
shaft. The spiral curves from behind forwards and 
inwards, and its axis is shghtly oblique to the long 
axis of the shaft. The inner lip is the more salient 
of the two, and forms a sharp and well-defined 
margin to the articular area ; its cartilage-covered 
surface is slightly convex. The outer lip, much 
less prominent, is rounded off into the articular 
groove which separates it from the capitellum, 
posterior to which, however, it is carried up as 
a more or less definite crest. 
for the 
| a 
Brachio-radialis 
_ EXT. EPICONDYLIC 
RIDGE 
Ext. carpi rad. longior 
EXT. EPICONDYLE 
Tendon of 
= 
extensors 
CAPITELLUM 
OLECRANON FOSSA 
\ 
Ext. LATERAL 
LIGAMENT 
TROCHLEA Anconeus. 
Fic. 132.—THE LOWER 
Richt HuMERUS AS 
THE OUTER SIDE. 
END OF 
SEEN 
THE 
FROM 
It is by means of the, trochlea that the 
