XIII 



PHYLUM CHORDATA 



515 



The scaphoid and lunar are united (Fig. 1101). 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 rudimentary in the Hyaena. 



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

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



7VV 



:i-"i<;. 1101. Carpus of Bear (Ursus ameri- 

 c//,> i(.s). c. cuneiform ; m. magnum; p. 

 pisiform ; v. s. radial sesamoid ; s. L 

 scapho-lunar ; t<l. trapezoid ; tm. tra- 

 pezium ; u. unciform. (After Flower.) 



FIG. 1102. The phalanges of the middle digit of 

 the maims of the Lion (Fdis Ico). ph l . proxi- 

 mal phalanx ; ph^. middle phalanx ; plfi. ungual 

 phalanx; a, the central portion forming the 

 internal support to the horny claw ; 6, 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 rudiment of the metatarsal. 



In the Pinnipedia (Fig. 1103) both acromion and coracoid are 

 short, 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 maims is broad and expanded. The scaphoid 

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

 are nearl} 7 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 vertebrae 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 most it is very short, but it is elongated in 

 some (the Porcupines, Squirrels and Beavers). The sternum of 

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

 broad pre-sternum ; the posterior end is always expanded into a 

 . cartilaginous xiphisternum. 



The skull is elongated, narrow in front, broader and depressed 



L L 2 



