XVI. 



crossed or capable of any considerable amount of rotation, as 

 in the cori-esponding 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 astrafagus, representing the coalesced scaphoid 

 and lunar of the hand, and the calcaneum. 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-cuneifonn, 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 sesamoid 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 SIKENIA and 

 CETACEA no traces of the third or distal segment of the hind limb 

 have been discovered, and only in certain members of the litter 

 Order have even rudiments of the proximal and median segments 

 been detected. 



