204 
is compressed from before backwards. 
from side to side, and is grooved in front for the sesamoid bones. 
Tubercle ( 
Ulnar side 
Trapezoid 
Fig. 150.—Seconpd METACARPAL 
is directed radial - wards. 
Superiorly there is a facet 
on the base for the os mag- 
To the radial side 
num. Uiner 
there are two half-oval side 
facets for the second meta- qnsertion 
carpal. To the ulnar side 
there are usually two small 
oval or nearly circular 
facets for the fourth meta- 
carpal. The extensor carpi 
radialis brevior muscle 1s 
inserted into the back of 
the base. 
The fourth metacarpal 
bone may be recognised by 
a method of exclusion. It 
is unlike either the first, 
second, or third, and 
\ Head 
Shaft 
of exten- Mi (f 
sor carpi -— i 
radialis 
brevior 
OSTEOLOGY. 
Its head, of large size,is but slightly convex 
The base is pro- 
vided with a saddle-shaped surface for articula- 
tion with the trapezium, and has no lateral 
facets. 
Externally there is a sight tubercle to 
which the abductor longus pollicis muscle is 
The canal for the nutrient artery 
is directed towards the head of the bone. 
The second metacarpal bone is recognised 
by its length and its broad and deeply-notched 
articulation with the trapezoid. It 
attached. 
base for 
SONE. 
fo 
FIG. 
‘ Trapezoid 
Radial side 
_»Trapezium 
has a small half-oval facet for 
the trapezium on the radial 
side of its base, whilst on its 
ulnar aspect it presents a 
narrow vertical strip for the 
oS Imagnum, in front of which 
there are two half-oval surfaces 
for the third metacarpal. To 
the dorsal aspect of the base 
is attached the tendon of the 
extensor carpi radialis longior 
muscle, whilst the flexor carpi 
radialis is inserted 
in front. 
The third meta- 
carpal bone can 
usually be recog- 
styloid process which 
springs from the 
back of its base, and 
Radial 
side 
151.—TuHtrbd METACARPAL BONE. 
differs from the fifth, which it resembles in size, by having articular surfaces on 
both sides of its base. 
articulation with the unciform. 
facets for the third metacarpal. 
has a narrow surface for articulation with the os magnum. 
Superiorly there is a quadrilateral surface on its base for 
On its radial side there are usually two small oval 
Of these facets the dorsal one not infrequently 
On the ulnar side 
there is a narrow articular strip for the base of the fifth metacarpal. 
The fifth metacarpal bone can be recognised by its size and the fact that it 
nised by the pointed’ 
