206 OSTEOLOGY. 
independent centre for the styloid process of the third metacarpal, and there is usually a 
seale-like epiphysis on the head of the first metacarpal which makes its appearance about 
eight or ten, and rapidly unites with the head. 
THE PHALANGES. 
ihe phalanges or finger bones (phalanges digitorum manus) are fourteen in 
for each finger, and two for the thumb. 
aad numerically i in order from the proximal toward the distal ends of the 
fingers, the first phalanx (phalanx prima), the longest and stoutest of the three, has a 
z semi-cylindrical shaft which is slightly curved forwards, 
The palmar surface is flat, and bounded on either side by 
two sharp borders to which the sheath of the flexor tendons 
is attached. The dorsal surface, convex from side to side, 
is overlain by the extensor tendons. The proximal end, 
considerably enlarged, has a simple oval concave surface, 
which rests on the head of its corresponding metacarpal 
bone. On either side of this the bone is tubercular, and 
affords attachment to the lateral ligaments of the meta- 
q carpo-phalangeal joint. The distal end is much smaller 
LL. Phalanx BR) than the proximal; the convex articular surface is divided 
. into two condyles by a central groove running from be- 
fore backward. ‘The second phalanx (phalanx secunda) 
resembles the first in general form, but is of smaller size. 
It differs, however, in the form of its proximal articular 
surface, which is not a simple oval concavity, but is an 
“Heal oval area divided into two small, nearly circular con- 
cavities by a central ridge passing from betore backwards ; 
these articulate with the condyloid surfaces of the proxi- 
mal phalanx. The third, terminal or ungual phalanx 
(phalanx tertia), is the smallest of the three; it is easily 
recognised by the spatula-shaped surface on its distal 
extremity which supports the nail. The articular surface 
on its proximal end resembles that on the proximal end 
of the second phalanx, but is smaller. On the palmar 
aspect of this end of the bone there is a rough surface for 
Base the insertion of the tendon of the flexor profundus digi- 
torum muscle. The phalanges of the thumb resemble 
in the arrangement of their parts the first and third 
phalanges of the fingers. 
II. 
Phalanx, 
ungual or 
terminal 
I. Phalanx 
Metacarpal 
Fra, 154..—THr PHALANGES OF 
THE FINGERS (palmar aspect). The arterial canals, usually two in nuwnber, placed on either 
side of the palmar aspect and nearer the distal than the proximal 
end of the bone, are directed towards the finger-tips. 
Architecture.—Each phalanx has a medullar y cavity, the walls of the shaft being formed of 
dense compact bone, especially thick along the dorsal aspect. The extremities are ‘made up of 
spongy bone within a thin dense shell. 
Variations.—Staderini has recorded a case in which there were three phalanges in the 
thumb (Inst. Anat. di Firenze G. Chiarurg Monitore Zool. Ital. Anno 5, N. 6-7, p. 119-128). 
Ossification.—The phalanges are ossified from primary and secondary centres. From 
the former, which appear as early as the ninth week of foetal life, the shaft and distal ex- 
tremities are developed ; whilst the latter, which begin to appear about the third year, 
form the proximal epiphyses which unite with the shafts from eighteen to twenty. Dixey 
(Proc. Roy. Soc. xxx. and xxxi.) has pointed out that the primary centre in the ungual 
phalanges commences to ossify in the distal part of the bone rather than towards “the 
centre of the shaft. This observation has been confirmed by Lambertz, who further 
demonstrates the fact that ossification commences earlier in the distal phalanges than in 
any of the other bones of the hand. Of the other phalanges, those of the first row, begin- 
ning with that of the third finger, next ossify, subsequent to the appearance of ossific 
centres in the shafts of the metacarpal bones, whilst the second or intermediate row of the 
phalanges is the last to ossify about the end of the third month. 
