ORDER ICHTHYOPTERYGIA. 



1123 



overlapping one another at their junction. The three bones of the 

 pelvis (fig. 1026, b) are weak and rod-like; the ilia have no con- 

 nection with the sacral region of the vertebral column • and although 

 the pubis and ischium of opposite sides meet in the middle line, 

 those of the same side do not unite to enclose the obturator notch. 

 The humerus and femur are relatively short ; but the radius and 

 tibia are still shorter, and may be reduced to oblong bones in 

 which the transverse diameter is the longer. 

 The humerus has no foramen. The struc- 

 ture of the paddles will be noticed under 

 the head of the different genera ; but it may 

 be observed that when there is a difference 

 in the size of the limbs it is the pectoral 

 that is the larger. From the less special- 

 ised structure of the limbs of the earlier 

 forms Dr Baur regards the Ichthyopterygia 

 as descendants of land animals ; a conclu- 

 sion which is supported by the argument 

 that had these Reptiles originated directly 

 from Fishes, as was formerly supposed to 

 be the case, they would have retained their 

 gills. In regarding this order as closely 

 allied to Sphenodon, Dr Baur lays stress 

 upon the general similarity in the cranial 

 structure, and especially the presence of 

 the foramen between the quadrate and 

 quadratojugal ; the identical structure of 

 the abdominal ribs ; and the remarkable 

 similarity of the pectoral girdle, which, this 

 author remarks, is only comparable to that 

 of the existing genus, especially when young. 

 In the skull and vertebral column the Ich- 

 thyopterygia retain evidences of their Laby- 

 rinthodont descent, which are lost in the 

 other orders of this branch. 



This order is known to range with cer- 

 tainty from the Upper Trias to the Upper 



Chalk. It was also widely distributed in space ; its remains having 

 been discovered in the Arctic regions, in Europe, India, Ceram, 

 North America, the east coast of Africa, Australia, and New 

 Zealand. Part of a jaw referred to Ichthyosaurus has been de- 

 scribed from Malta, which, it has been suggested, may be of 

 Miocene age, but this requires confirmation. 



It may be remarked that the humerus and femur of this order 

 are quite unique in that, instead of having convex condyles for the 



Fig. 1026 bis. — Proximal, 

 dorsal, and distal aspects of 

 the left humerus of Ichthyo- 

 saurus ; from the Kimeridge 

 Clay. One-third natural size. 

 a, Trochanteric ridge ; r, Fa- 

 cet for radius ; u, Do. for 

 ulna. 



