REPTILES. 209 



union of the iliac bones, the ischiadic and pubic bones are placed, 

 forming together a round, laterally compressed disc. In the Saurians 

 the pelvis is usually more perfectly formed ; the three bones, which 

 compose it on each side, meet each other at the articular cavity for 

 the thigh-bone, and the ischiadic bones unite behind the junction 

 of the pubic bones, whilst between these two unions a very large 

 aperture remains. Often the resemblance is here very striking to 

 the osseous belt formed by the two clavicles and the scapula. 



In the Ophidians no limbs are present, except only in the genus 

 Chirotes, in other respects so similar to Amphisbcena, where short 

 anterior limbs occur, and except the traces of hind limbs which are 

 found hidden beneath the skin in many serpents, either wholly, or 

 with the exception of the conical nail-joint. The rest of the 

 reptiles have, on the other hand, very commonly four limbs, mostly 

 provided with five fingers, and on the whole composed upon the 

 same fundamental plan as in the mammals. The upper-arm bone 

 and the thigh-bone are however directed outwards, whence the 

 elbow and knee-joints are at a distance from the trunk. The bones 

 of the carpus are more numerous than those of the tarsus. In the 

 anterior extremities of the frogs, the place of radius and ulna, 

 as in the hinder extremities that of tibia and fibula, is occupied by 

 a single bone ; yet even externally, but more obviously when it is 

 sawn across, it may be seen that two bones which have coalesced 

 compose that single bone. 



On the bones of the head it is difficult to say anything general. 

 The occipital bone in batrachians consists principally or exclusively 

 of two lateral pieces, which meet above and below, and so surround 

 the occipital hole. Each of these lateral occipital bones has an 

 articular tubercle, which is connected with the first vertebra. In 

 the scaly reptiles, the serpents, lizards and tortoises, the articular 

 tubercle serving for connexion with the atlas is, on the contrary, 

 placed in the middle under the large occipital foramen, as it is in 

 birds, and is principally formed by the basal piece of the occipital 

 bone, and only in part by the lateral occipitals, which close upon 

 it. A large part of the cranium in the frogs continues mem- 

 branous or cartilaginous. The base of the cranium is formed almost 

 exclusively of the flat body of the sphenoid. The other cra- 

 nial bones are very aberrant and various ; they are, as in fishes, 

 more numerous than in mammals. The temporal bone is always 



VOL. II. 14 





