THE SKELETON OF REPTILES 39 



known as the scaphoid, lunar, cuneiform, and pisiform. The second 

 row has but two bones, on the radial side, known as the centralia; 

 while the third row has a bone to correspond to each of the meta- 

 carpals, five in number, and collectively known as the carpalia. 

 Some or indeed all of these bones may be either absent or unossified, 

 that is, remaining through life as nodules of cartilage. Seldom, 

 however, are there less than nine bones in the carpus of reptiles. 



The metacarpals, like the digits, primitively were five in number, 

 and seldom are there less, though the fifth is sometimes lost, and 

 rarely also the first. They are more or less elongate bones, increas- 

 ing in length from the first to the fourth, with the fifth usually 

 shorter. The first and the fifth are usually more freely movable 

 on the wrist than are the other three. 



The number of joints or phalanges in the fingers of all primitive 

 reptiles is that of the modern lizards and the tuatera, that is, two 

 on the first finger or thumb, three on the second, four on the third, 

 five on the fourth, and three on the fifth. The crocodiles have one 

 less phalange on the fourth digit; the turtles have usually two 

 less on the fourth and one less on the third, that is, with precisely 

 the same arrangement that is found in our own fingers and that of 

 mammals in general, two on the thumb and three on each of the 

 other fingers. As exceptions the river turtles have four bones in 

 the fourth digit. And this mammal-like and turtle-like arrange- 

 ment of the phalanges was that of those early reptiles, the Therio- 

 dontia, from which the mammals arose. The last or ungual 

 phalange of reptiles is usually claw-like, that is, sharp, curved, 

 and pointed, but sometimes it is more nail- or hoof-like. 



PELVIC OR HIP GIRDLE 



The pelvic girdle or pelvis in reptiles and higher animals con- 

 sists of three bones on each side, often closely fused in adult reptiles 

 and together known as the innominate bone. The upper or dorsal 

 one of these three bones— that to which the sacrum is attached— 

 is the ilium; the one on the lower or ventral side in front is the 

 pubis; and that on the ventral side behind is the ischium. On 

 the outer side, where these three bones meet, is a cup-like depres- 

 sion, sometimes a hole, called the acetabulum, for the articulation 



