of Vertebra from Cape Colony. 343 



being- absorbed laterally. But the lung never penetrates into 

 the substance of the vertebra or excavates holes in the bones 

 in existing reptiles comparable to those seen in skeletons of 

 Dinosaurs, Ornithosaurs, and birds. 



The influence of the lungs on the vertebral column of a 

 Dinosaur as distinct from the air-cells may be, perhaps, 

 inferred from the elevated condition of the neural arch and 

 upward direction of transverse processes under whicli the 

 lungs extended in such a type as Diplodocus, described by 

 Prof. Osborn and the late Dr. J. B. Hatcher. It is reasonable 

 to infer that the lungs were so large that their intermittent 

 upward pressure stimulated the growth of the neuro-central 

 suture to form the high neural arch ; but as they were not 

 confined by an unyielding envelope in the same way that the 

 carapace confines the lungs of tortoises, there is but little 

 lateral compression of the body of a vertebra as a conse- 

 quence of absorption, which was localized laterally about the 

 pneumatic foramen. 



All down the vertebral column in Diplodocus the vertebrae 

 are excavated, and the lateral holes were termed by Dr. 

 Hatcher pleuro-central cavities. They have been well 

 described in Ornithopsis. Their distinctive feature is that in 

 the dorsal region the lateral foramina expand within the 

 centrum into large chambers separated by a median vertical 

 longitudinal partition, and each is commonly divided into 

 unequal anterior and posterior parts by an imperfect vertical 

 transverse lamina of bone. From this primary lateral cavity 

 bone-cells commonly extend to the articular faces of the 

 centrum and other parts of the vertebra. This condition of 

 the pneumatic vertebraj is only dissimilar to that of birds in 

 its details. In no existing animals except birds is a similar 

 pneumatic structure found in the vertebral column, and it is 

 only known in connexion with air-cells prolonged from the 

 lungs. There is no fact to suggest that the lungs themselves 

 were extended into the pleuro-central cavities of Dinosaurs : 

 such an idea is not consistent with the pneumaticconditionof the 

 vertebrae in the elongated neck and tail. But with the general 

 resemblance to the condition in the bones of birds it has been 

 inferred that the pneumatic pressure, which was persistent 

 enough to absorb tlie bone locally and laterally, was greater 

 in Dinosaurs than in birds, because the cavities excavated 

 are larger. Although this pressure, judged by its effects, was 

 most potent in the dorsal region of the lungs, it also extended 

 to the neck and tail, as in certain birds. It is therefore 

 inferred that no cause is known except prolongation of air- 

 cells from the lungs into the bones which is capable of 



