XIII 



PHYLUM CHOPvDATA 



547 



The scaphoid and lunar are united (Fig, 1170). There is no 

 centrale. Usually a radial sesamoid is present. There are five 

 digits, though the pollex may be reduced in size, as in the Dog, 

 and it is vestigial in the Hyii-na. 



The pehis is long and narrow. In the tarsus all the ordinary 

 bones are developed. The hallux is fully formed in the Bears, &c., 



Fig. 1170.— Carpus of Bear {Ursus ameri- 

 caiiun). c. cuneiform ; hi. magnum ; p. 

 pisiform ; r. s. radial sesamoid ; n. I. 

 scapho-lvuiar ; td. trapezoid ; im. tra- 

 pezium ; V. unciform. (After Flower.) 



Fig. 1171.— The phalanges of the middle digit of 

 the manus of the Zjion (^Frlh feo). phi. proxi- 

 mal phalanx;/;/,-, middle phalanx; /j/i^'. ungual 

 phalanx ; a, the central portion forming the 

 intern.'d support to the horny claw ; b, the 

 bony lamina reflected around "the base of the 

 claw. (After Flower.) 



but shorter than the other digits, In the Cats and Dogs it is 

 represented only by a vestige of the metatarsal. 



In the Pinnipedia (Fig. 1172) both acromion and coracoid are 

 short, and the scapula is curved backwards ; there is no clavicle. 

 The bones of the fore-limb are short and stout; the humerus has 

 a prominent deltoid crest ; there is no foramen above the inner 

 condyle. The ulna is greatly expanded at its proximal, the radius 

 at its distal end. The manus is broad and expanded. The scaphoid 

 and lunar are united to form a scapho-lunar. The ungual phalanges 

 are nearly straight, slender, and pointed. The ilia are short ; the 

 symphysis pubis is short and without firm union of the bones. 

 The femur is short, thick, and flattened. The fibula and tibia are 

 commonly ankylosed proximally. The calcaneum is short and 

 usually without a distinct calcaneal process ; the lateral digits are 

 usually the longest. 



Skeleton of the Rodentia. — Among the Rodents the Jerboas 

 are exceptional in having the cervical vertebniB ankylosed. Gene- 

 rally, as in the Rabbit, the transverse processes of the lumbar 

 vertebrae are elongated. As in the Ungulata, the sacrum usually 

 consists of one broad anterior vertebra followed by several 



narrower ones. The caudal 



region 



varies in length in the 



different families ; in some it is very short, but it is elongated in 

 many (the Porcuijines, Squirrels, and Beavers). The sternum of 

 the Rodents has a long and narrow body ; sometimes there is a 

 broad presternum ; the posterior end is always expanded into a 

 cartilaginous xiphisternum. 



