242 OSTEOLOGY. 
the cartilaginous elements of the os calcis and astragalus, and the os calcis and navicular in 
foetuses of the third month. 
Ossification.— Unlike the carpus, the tarsus is at birth partially ossified. At this 
period there is a well-marked osseous nucleus within the body and neck of the astragalus, 
and the os calcis is extensively ossified. In the latter the deposition of earthy matter 
appears as early as the sixth month of foetal life, whilst in the astragalus the ossifie centre 
makes its appearance in the later weeks of gestation. Shortly before or after birth the 
cuboid begins to ossify, succeeded early in the first year by the external cuneiform, followed 
in order by the middle cuneiform, internal cuneiform, and navicular. The ossific centre 
of the latter appears at the third year or somewhat later. An epiphysis, which forms a 
cap over the extremity of the great tuberosity of the os calcis, appears from the seventh to 
to the ninth year, and fusion is completed between the ages of sixteen and twenty. 
THE METATARSUS. 
The metatarsal bones, five in number, in their general configuration resemble 
the metacarpus. They are, however, slightly longer, their bases are proportionately 
larger, their shafts more*slender and laterally compressed, and their heads propor- 
tionately smaller. They are named numerically the first, second, third, fourth, and 
fifth metatarsal bones, in order from within outwards. The first can be readily 
recognised on account of its stoutness; it 1s also the shortest of the series. The 
second is the longest of the five, and the fifth can easily be distinguished by the 
projecting tubercle at its base. 
The first metatarsal or metatarsal bone of the great toe, the shortest of the 
series, 1s remarkable for its stoutness. The vertical diameter of its base much 
exceeds its transverse width, here the bone is provided 
with a reniform facet for articulation with the internal 
cuneiform. Asarule there are no facets on the lateral 
aspects of the base. The inferior angle projects backwards 
and outwards, and forms a prominent tubercle which is 
jHea pitted for the insertion of the tendon of the peroneus 
longus muscle, whilst its internal margin is lipped by a 
surface for the attachment of part of the tendon of the 
tibialis anticus. The shaft, short, thick, and prismatic on 
section, tapers rapidly towards the head, the fore and 
under surfaces of which are articular. The former is con- 
vex from side to side, and from above downwards, and 
supports the proximal phalanx. It is confluent below 
with the inferior articular surface, which is divided by a 
median ridge into two shallow grooves of which the inner 
is the wider. In these grooves are lodged the two sesa- 
pass moid bones which underlie the metatarso - phalangeal 
joint. On either side of the head, the bone is pitted for 
the strong lateral ligaments of the joint. 
vo ee are The second metatarsal, the longest of the series, has 
Mi a base of wedge-shaped form, the proximal aspect of which 
Fic. 189.—THe First MeETs- __|- S bao ae : 5 : 
TARSAL BONE OF THE Ricut 2Fticulates with the middle cuneiform. On its inner 
Foor (plantar aspect). aspect, near its superior edge, there is a small circular 
facet for the internal cuneiform; below and in front of 
this there is sometimes a tubercle with a “pressure” facet on it, where the bone 
comes in contact with the base of the first metatarsal. On the outer side of the 
base there is one, more usually two facets, each divided into two parts, a posterior 
for articulation with the external cuneiform, and an anterior for the base of the 
third metatarsal. The shafts of this and the three succeeding bones are slender 
and laterally compressed. The heads are small and narrow, and display a pro- 
nounced side-to-side and vertical convexity. 
The third metatarsal bone also possesses a base of wedge-shaped form, the 
proximal surface of which articulates with the external cuneiform. On its inner 
side it is provided with one, more usually two small facets, for articulation with the 
base of the second metatarsal. Externally the base has a larger facet for articula- 
GROOVES FOR SESAMOID BONES 
II. METATARSAL 
