106 REPORT— 1889. 



for bringing the head to the surface of the water for the purpose 

 of breathing is the same in both the Monotreme and the Ceta- 

 cean, viz. a strong, muscular, horizontally flattened tail. In 

 the Ichthyosaunis a pair of hinder paddles (which in the large- 

 headed species, as the Ich. platyodoji, are equal in size with 

 the fore paddles,) must have fully compensated for that dif- 

 ferent construction of the tail, which, while it rendered it less 

 efficient as a means of raising the head to the surface, made it a 

 more perfect instrument in ordinary natation ; and the suf- 

 ficiency of this compensation will be better appreciated when it 

 is remembered that the Reptilian structure of the lungs and 

 heart of the Ichthyosaurus would allow it to dispense with so 

 perfect a machinery for rising to the surface as was essential to 

 the warm-blooded aquatic species above cited. 



For what purpose then were sterno-clavicular and coracoid 

 arches assigned to the Ichthyosaurus ? Doubtless that the ante- 

 rior paddles might be subservient to locomotion not only in the 

 water but on land ; and that, when applied to the resisting soil, 

 they might react with due force upon the trunk. It is very con- 

 ceivable that the Ichthyosaurus like the Crocodile mayhave come 

 ashore to sleep : it is most probable that they resorted to the 

 shore to deposit their eggs, supposing them to have been ovi- 

 parous, as the sum of the analogies deducible from their osseous 

 texture would indicate. The hind paddles would also be ser- 

 viceable in terrestrial progression as in the Ornithorhynchus^ 

 while ill the strictly marine Cetacea they could readily be dis- 

 pensed with. 



The radiated bones of the anterior extremities consist of a 

 distinct humerus, radius and ulna, carpal, metacarpal, and pha- 

 langial bones. 



Both the brachial and antibrachial bones of the Ichthyosaurus 

 are much shorter and broader in proportion to their length than 

 are the corresponding bones of the Plesiosaurus. This is more 

 particularly the case with the radius and ulna, which are usually 

 broader than they are long, and closely resemble the carpal 

 bones which succeed them. The limits of the carpus can be by 

 no means so easily defined as those of the antibrachium. The 

 first row of bones which succeeds to the radius and ulna includes 

 three polygonal or rounded flat bones, generally broader than 

 they are long ; the next row includes three or four similar bones ; 

 and then instead of being succeeded by elongated metacarpals 

 and phalanges, as in the Plesiosauri, the fin is supported by 

 numerous rows of smaller but similarly-shaped flattened ossicles, 

 increasing in number as they diminish in size, to near the extre- 

 mity of the paddle. These small flattened ossicles are arranged 

 in from three to six digital series, and are generally dovetailed 



