XVi. 
crossed or capable of any considerable amount of rotation, as 
in the corresponding bones of the antibrachium. In many 
Mammals the fibula is rudimentary, and in some, as certain 
ruminants, it forms, in old animals, a more or less complete 
ankylosis with the tibia. A large sesamoid bone, known as the 
knee-cap or “‘patella,” is developed in the tendon of the extensor 
muscle of the thigh, in front of and for the protection of the 
knee-joint, and is present in an ossified condition in all Mammals, 
excepting some of the Marsupials. 
Foot.—The terminal segment of the hind limb, like that of 
the fore limb, consists of three parts, of which the proximal is 
termed the tarsus, the median the metatarsus, and the distal the 
phalanges. In the tarsus the proximal series always consists of 
two bones, the astra/agus, representing the coalesced scaphoid 
and lunar of the hand, and the ca/ecaneum. The former is placed 
more to the dorsal side of the foot, and almost exclusively 
furnishes the tarsal portion of the ankle joint; the latter is 
situated more towards the plantar side of the foot, and is 
elongated backwards to form a more or less prominent tuberosity 
(the heel) to which the tendon of the great extensor muscles of 
the foot is attached. The navicular bone is interposed between 
the proximal and distal series on the inner side of the foot, thus 
leaving the two series in contact on the outer side. The distal 
series, when complete, contains four bones, which, beginning as 
usual on the inner side, are the three cuneiform, the internal 
being known as the first or ento-cuneiform, the median as the 
second or meso-cuneiform, and the external as the third or ecto- 
cuneiform ,; of these the second is the smallest, and all three are 
articulated to the distal surface of the navicular ; the fourth bone 
is the cuboid, and articulates with the calcaneum; in Mammals 
where the hallux is wanting, the ento-cuneiform may be rudi- 
mentary or altogether absent. The three cuneiform bones support 
the first, second, and third metatarsal bones, and the cuboid the 
fourth and fifth ; as in the hand sesamozd bones are developed in 
addition to the constant bones of the tarsus. The formation of 
the phalanges of the foot is in all respects similar to that of the 
hand, and, with the one exception of the inner digit—which is 
termed the hallux, and corresponds to the pollex of the hand— 
the names applied to the other digits of the foot are the same as 
those by which the corresponding digits of the hand are known. 
In the hallux, as in the pollex, one bone of the normal mamma- 
lian four—including the metacarpals and metatarsals—is wanting, 
and it is still a disputed question whether the missing bone is the 
first metatarsal, or the proximal phalanx. In the Srrenra and 
Ceracea no traces of the third or distal segment of the hind limb 
have been discovered, and only in certain members of the 1]: tter 
Order have even rudiments of the proximal and median segments 
been detected. 
