300 



VERTEBRATE SKELETON 



separate; carpus and tarsus are almost perfectly taxeopodous, and each has a 

 centrale. The three middle digits of the manus are subequal; i and 5 much 

 smaller, the latter having three phalanges. The axis of the foot is as in Peris- 

 sodactyls. The femur has a small third trochanter; the fibula is entire and 

 largest distally where it fuses with the tibia and articulates with the talus. The 

 hind feet are three-toed, the hallux being absent and 5 represented by a small 

 metatarsal nodule. 



Proboscidia have the head of the humerus scarcely separated from the 

 shaft by a neck, and no epicondylar foramen. Radius and ulna are separate, 

 the latter complete, its distal end the larger. The carpus (fig. 323) is completely 

 taxeopod; the centrale fuses with the radiale in the young, but the other carpal 

 bones remain separate. Carpale i resembles a short metacarpal. The meta- 

 carpals and the digits of the semiplantigrade feet are short. The short femur 



Fig. 323. Fig 324. 



Fig. 323. — Fore foot of elephant (Flower and Lyddeker, '91). c, triquetrum 

 (ulnare); I, lunatum (intermedium); w, magnum (carpale 3); R, radius; 5, naviculare 

 (radiale); /, <rf. trapezium and trapezoid (carpalia i and 2); C7, ulna; «, hamatum (carpalia 

 4 and 5). 



Fig. 324. — Tarsus of Tarsius (Burmeister, Weber, '04). c, calcaneus; O \ ento- 

 meso-, and ectocuneiformia; cd, cuboid; s, scaphoid. 



has no third trochanter; tibia and fibula are separate, the latter slender and 

 articulating with the calcaneus. The tarsus is almost perfectly taxeopod and 

 the hind feet are very similar to those in front. 



SiRENiA have the fore limbs well developed, the hinder pair vestigial or lost. 

 The fore limbs differ considerably from those of whales, with which these animals 

 were formerly associated, in the extent and freedom of the joints. The humerus 

 has the tuberosities distinct in Halkorc and Rhytina, and its lower end has a well- 

 developed trochlea and a moderate olecranon fossa. Radius and ulna, nearly 

 equal, are fused at either end. The manus is nearly normal, most of the bones 

 being separate in Manatus, the carpalia largely fused in Halicore. The five 

 digits have the normal phalangeal formula. No traces of a free hind limb exist 



