428 



Vertehrata. 



short. Among other characters, it may he mentioned, that the sclerotic of 

 the large eye was provided with a ring of bony plates ; the vertebral centra 

 wei'e veiy large and strongly biconcave, the pelvis was not connected with the 

 vertebral column, the hind limbs weaker than the fore, the teeth in a continuous 

 fui-row in the edge of the jaw, a character which also occurs in several other 

 animals {e.g., certain Whales). The Ichthyosam-ians were marine, some of very 

 gi-eat size (10 m. and more) ; they lived in Trtassic, Jvu-assic, and Cretaceous 

 times. 



The Flesiosaurians, another extinct type of mai-ine Reptile, are in some 

 I'espects like the Ichthyosaui-ians, in others veiy different from them. The 

 head is small, sometimes even very small ; the neck, on the contrary, is long ; 

 longest in those with the smallest head. The compressed piscine form of body 

 which obtains in the Ichthyosaurians is absent here. Fore and hind limbs. 



Fig. 353. A Plesiosaiirian. 



as in the latter, are clawless, and like the fins of a Whale ; they are, however, 

 xisually larger than in the Ichthyosauj-ians, the bones are not so much shortened, 

 and the number of digits does not exceed five. They attaia a length equal to 

 that of the Ichthyostarians. Triassic, Jtu-assic, Cretaceoiis. 



A Pteroclactyle, restored. — Modified 



The Fterodactyles {Pterosauria : genera Ptero- 

 dactylus, Bamphm-hynchus, etc.), were specially 

 characterised by the modification of the fore limbs 

 as actual organs of fiight. Each fore limb had four 

 digits, of which the thi-ee inner (Nos. 1, 2, 3), were 

 not pai-ticularly developed, whilst the fourth, next 

 to the middle finger, was much elongated, and formed 

 the edge of the large patagium; this membrane, 

 of which several impressions have been found, was 

 stretched from that finger to the body. The head, 

 especially the anterior pait, is of considei-able size ; 

 in the sclerotic there was a bony ring ; teeth are 

 usually present and placed in sockets ; the sternum 

 is provided with a keel, possibly for the attachment 

 of the pectoral muscles, which moved the vrings ; the 



