192 OSTEOLOGY. 
The inferior extremity of the ulna presents a rounded head (capitulum ulnee), 
from which, on its inner and posterior aspect, there projects downwards a cylindrical 
OLECRANON PROCESS 
GREAT SIGMOID CAVITY 
Flexor 
sublimis 
“digitorum 
Pronator 
_7yYadii teres 
CORONOID PROCESS\_ 
Brachialis anticus 
SMALL SIGMO1D 
CAVITY 
Flexor longus 
pollicis 
TUBEROSITY 
Biceps 
; BIcIPITAL HOLLOW 
Supinator 
radii brevis 
TUBEROSIT Y ——- 
| 
Supinator 
radii brevis - 
ANTERIOR 
OBLIQUE 
LINE 
ARTERIAL 
FORAME 
ARTERIAL__ Ras 
FORAMEN 
Flexor 
ee INTEROSSEOUS 
sublimis BORDER 
digitorum ; , 
Vh 
Pronator H 
radii teres | 
i 
INTEROSSEOUS 
BORDER 
Pronator 
quadratus 
Pronator 
quadratus 
Brachio- 
radialis ‘| —-~HEAD 
STYLOID 
PROCESS 
Sryiorp } 
PROCESS 
Fie. 135.—THE Rapius AND ULNA AS SEEN FROM THE FRONT. 
pointed process called the styloid 
process (processus styloideus). 
To the extremity of this latter 
is attached the external lateral 
ligament, whilst in front it has 
connected with it the antero- 
internal portion of the capsule 
of the wrist joint. The antero- 
external half of the circum- 
ference of the head is furnished 
with a smooth narrow convex 
articular surface, which fits into 
the sigmoid cavity of the radius. 
Its inferior surface, flat and 
semilunar in shape, and separ- 
ated from the root of the styloid 
process by a well-marked groove, 
rests on the upper surface of 
the triangular fibro - cartilage 
of the wrist, the apex of which 
is attached to the groove just 
mentioned. The margins of the 
head in front and behind the 
radial articular surface have 
attached to them the anterior 
and posterior inferior radio- 
ulnar ligaments. The hinder 
and outer surface of the styloid 
process is channelled by a groove 
which separates it from the 
posterior surface of the head, 
and extends some little way up 
the posterior aspect of the lower 
end of the shaft. In this is 
lodged the tendon of the ex- 
tensor carpi ulnaris muscle. 
The proportionate length of the 
ulna to the body height is as 
1 is to 6:26-6:66. 
Nutrient Foramina.— <A _ fora- 
men, having an upward direction 
for the nutrient artery of the shaft, 
opens on the anterior surface of the 
bone from two to three inches below 
the tuberosity. Vascular canals of 
large size are seen above and behind 
the small sigmoid cavity, just pos- 
terior to the notched external border 
of the great sigmoid cavity. At the 
lower end of the bone similar open- 
ings are seen in the groove between 
the styloid process and the inferior 
articular surface of the head. 
Connexions.—The ulna articu- 
lates above with the trochlea of 
the humerus. On the outer side it 
is in contact with the radius above and below, the superior radio- ulnar articulation being 
formed by the head of the radius and the small sigmoid cavity of the ulna, the inferior radio- 
whar joint comprising the head of the ulna, which fits into the sigmoid cavity of the radius. 
Between these two joints the shafts of the bones are united by the interosseous membrane. 
The 
