FOSSIL REPTILES. 371 



head, or at least the number of those which have any besides 

 a tubercle, must have been very small. This head of the rib 

 articulates with the extremity of the transverse apophysis, 

 which is sometimes concave, sometimes convex, though it is 

 not possible to assign the place of the vertebrae which have 

 these separate conformations. In the groups examined by the 

 Baron, near the vertebrae in which the end of the transverse 

 apophysis is convex, ribs were found whose heads were con- 

 cave, and vice versa. 



These ribs, in the greatest part of the back, appear to have 

 been composed, each of two parts, a vertebral and a ventral, 

 and it is judged, from the skeleton of Lyme, that the ventral 

 part of one rib was united to that of the opposite rib, by an 

 intermediate cross-piece. So that each pair of ribs (the 

 sternal, if any excepted) surrounded the abdomen by a com- 

 plete cincture, and this cincture was composed of five piece?. 

 The cameleons, the marbres, and the anolis, have also the 

 belly surrounded by complete circles, which would lead us to 

 conjecture that the lungs of the plesiosaurus, like those of these 

 three subgenera, were very much extended, and, perhaps, 

 like them, unless the scales were very thick, it changed the 

 colour of its skin according to the greater or less force of its 

 inspiration. 



Mr. Conybeare, in his restored figure of the plesiosaurus, 

 makes the simple ribs, not terminated in the hatchet-form, to 

 commence at the thirty-seventh vertebra. He marks seven on 

 each side which go on increasing in size, but have no ventral 

 part. Then he gives fourteen with this ventral part — then 

 three which want it — and further back he places four lumbar 

 vertebrae without ribs. 



The humero-sternal apparatus was, in a great measure, re- 

 established by Mr. Conybeare, at the time he wrote his first 

 notice of this animal. 



What is most remarkable here, is the coraco'id bone, which 

 is more dilated into a fan-like form than in any other saurian, 



2 B 2 



