BETWEEN TYPICAL REPTILES AND OTHER ANIMALS. 161 



as in some other parts of the skull, the Crocodile comes less near 

 to birds than to mammals. A ligament extends from the post- 

 frontal process to the malar bone in birds, and represents the 

 osseous connexion between those bones which characterize Cro- 

 codiles and ruminant mammals. If a similar ligament united the 

 distal end of the squamosal with the postfrontal in birds, it 

 would enclose superior temporal fossae, which in Crocodiles hare 

 osseous boundaries. 



The lower jaw of the Crocodile is more like that of a bird than 

 a mammal, being composite, perforated posteriorly, and having 

 the articular element much developed on the inner side of the 

 articulation, owing to the width of the articular end of the qua- 

 drate bone. In the Crocodile the bones are placed differently 

 from the arrangement in birds, and the dentary rami remain 

 separate. In view of some structures in fossil animals, it may be 

 mentioned that in some birds the squamosal bone has a ligamen- 

 tous, almost osseous, union with the quadrato-jugal. 



The vertebral column in birds is in many respects unlike that 

 of Crocodiles. Instead of the cup-shaped articular centrum, the 

 bird has it merely concave from side to side, and never from above 

 downward ; while a few birds — Penguins — present the mamma- 

 lian and chelonian type of having some vertebrae opisthocoelous. 

 There are more vertebrae in the neck of birds than in that of 

 Crocodiles, no bird being reported to have fewer than the 

 Sparrow, in which Cuvier counted nine, and Prof. Owen twelve, 

 while there may be twice that number ; no bird has unanchylosed 

 cervical ribs comparable to those of Crocodiles. 



The dorsal vertebrae are fewer in number in birds than in the 

 Crocodile ; but the upper head of the rib is similarly supported 

 on a transverse process, while the lower is uniformly attached to 

 the centrum — an arrangement which only obtains in the Crocodile 

 in the vertebrae which I name pectoral. 



The sacral vertebrae of Crocodiles are unlike the sacrum of 

 birds in never including more than two or three vertebrae which 

 remain unanchylosed. In many birds the sacral elements simi- 

 larly have transverse processes ; 'but in Crocodiles they are sepa- 

 rate bones, while in birds they are anchylosed with the centrums. 



The caudal vertebrae of Crocodiles are much more numerous 

 and much longer than in living birds. In birds tlie articular (ace 

 of the centrum is usually flat or slightly concave in front aud 

 convex behind, while, where they exist, the anterior zygapophyses 



