OEGANIZATION OF THE OENITHOSAUEIA. 93 



wliieli eacli gives off at right angles. The branches appear to be 

 best seen in the transverse section, where many can be traced ex- 

 tending in a wavy course for some distance at right angles to the 

 tube from which they are given off. The branches are sometimes 

 as large as the principal tubes, which, towards the outer part of the 

 tooth run straight. In the transverse section (PI. XI. fig, 12) the 

 branches appear to unite the tubes together much as the principal 

 tubes are united in some Carboniferous species of the corslSyrmgo- 

 pora; but this appearance is probably delusive. The enamel is very 

 thin, and only distinguished from the dentine by being perfectly 

 translucent ; but calcigerous tubes are continued into it without 

 any break. Exactly the same kind of structure has not been 

 figured, so far as I know, in any existing animal. It reminds me 

 of that attributed by Professor Owen to Saurocejplialus ; but iu 

 this fish, which has a similar form of tooth, the tubes are fewer 

 beyond comparison. Among reptiles, there is a resemblance in 

 the number of tubes to Iguana. Cetaceans and bats indicate 

 structural resemblances probably as close, though in those ani- 

 mals the tubes are fewer. 



The only remaining points of importance in the skull are that 

 the eyes usually, if not always, abut against the anterior walls of 

 the brain-case, as they do in some birds, and that the skull is 

 articulated at right angles to the vertebral column, as it is in all 

 birds. Perhaps little importance should be attached to this latter 

 character, although it is found in no reptile, because in Ceta- 

 ceans the head is in a line with the vertebral column, as it is in 

 reptiles, while in the fish Hippocampus the head is placed at an 

 angle to the vertebral column, as it is in birds. 



Finally, every point of the Ornithosaurian skull upon which 

 I have not offered comment presents absolute identity with the 

 corresponding structures in birds. I now pass them over, not 

 because their great weight should be overlooked in an attempt to 

 estimate the osteology of the group, but because there are no new 

 facts to be adduced in addition to those given in previous writings 

 on the subject. 



On the whole, I do not regard the Pterodactyle's skull as dif- 

 fering from the bird's skull to any thing like the same extent 

 ,as the skulls of birds, or of Pterodactyles, differ from each 

 other. 



The vertebral column presents considerable variety in the 

 -Ornithosauria. Owing to the conditions of fossilization, the nam- 



