xii PHYLUM CHORD AT A 339 



cartilages which are so arranged as to support the thin 

 broad expanse of the fin. 



In both the Lizard and the Rabbit the skeleton of the 

 limbs is constructed on a general plan, common to the 

 limbs of all Craniata but the Fishes, and known as the 

 pentadactyle (Fig. 200), in allusion to the five digits in 

 which the limb typically terminates. In the pectoral limb 

 (A) the upper arm has a single long bone known as the 

 humerus \ at its proximal end this is movably articulated 

 with the pectoral arch. The forearm contains two long 

 bones radius and ulna articulating proximally with the 

 distal end of the humerus. The skeleton of the hand con- 

 sists of three principal parts the carpus, the metacarpus, 

 and the phalanges. The carpus or wrist consists of a 

 number of small irregularly-shaped bones arranged in two 

 transverse rows, proximal and distal, with a central bone 

 between the rows. The metacarpus consists of five (Lizard) 

 narrow bones forming the support of the basal parts of the 

 digits, and articulating proximally with the distal row of 

 carpals. The rest of the skeleton of the digit is formed of 

 a row of small bones, the phalanges, the last of which 

 ungual phalanx is modified in shape to support the horny 

 claw. 



The skeleton of the hind-limb (B) corresponds closely 

 with that of the fore-limb. The pelvic arch consists on each 

 side of three bones which become firmly united together, one 

 of these, the ilium, is dorsal in position, the other two, pubis 

 and ischium, are ventral, the pubis being anterior to the 

 ischium. The ilia articulate firmly with the sacral region 

 of the spinal column; the pubes unite ventrally in an 

 articulation known as the pubic symphysis, and in the 

 Lizard the ischia are similarly connected. Laterally, 

 where the three bones unite, is a cup-like cavity the 



z 2 



