THE SKELETON IN REPTILES. PELVIC GIRDLE. 291 



possesses both ent- and ect-epicondylar foramina. The radius 

 and ulna are always separate. In some Chelonia, such as 

 Chelydra, the carpus has a very simple arrangement, namely, 

 a proximal row of three bones, the radiale, intermedium and 

 ulnare, and a distal row of five carpalia, with one bone, the 

 centrale, between the two rows. Many reptiles have a carpus 

 only slightly different from this. Thus the carpus in Spheno- 

 don differs mainly in having two centralia, that of most Lacer- 

 tilia, in having the centrale and intermedium fused. 



Crocodiles have a much reduced carpus with the radiale 

 and ulnare considerably elongated. The manus in Chamaeleons 

 is curiously modified, having the first three digits arranged in 

 one group and turned inwards, and the fourth and fifth in 

 another group turned outwards ; carpalia 3 and 4 are united. 



In the Pterosauria the anterior limbs form wings, the 

 phalanges of the fifth digit being very greatly elongated to 

 support the wing membrane. The first digit is vestigial and 

 the second, third, and fourth are clawed. 



THE PELVIC GIRDLE. 



The pelvic girdle is well developed in all reptiles which 

 have posterior limbs, but is absent or quite vestigial in Ophidia 

 and those Lacertilia which have no posterior limbs. The ilium 

 and ischium agree in their general characters throughout all 

 the various groups of reptiles, but that is not the case with 

 the pubis. 



In many reptiles such as Chelonia, Ichthyosauria and 

 Lacertilia the ilia are small, more or less cylindrical bones 

 either directed backwards, or vertically placed as in the 

 Chamaeleons. In the Crocodilia they are larger and more ex- 

 panded, while in Dinosauria and Pterosauria they are greatly 

 elongated both in front of, and behind, the acetabulum. The 

 ischia are generally strongly developed somewhat square bones 

 meeting in a ventral symphysis. In Dinosauria the ischium 

 (fig. 35, 9) is a much elongated and backwardly-directed bone, 



192 



