No. 525] THE SAUR0P0D0U8 DINOSAURS 553 



In a brief description of the Brontosaurus skeleton 2 

 which Dr. Hay consistently ignores, although he can 

 hardly fail to be acquainted with it, the reviewer pointed 

 out that there was a very marked difference in the mas- 

 siveness of the upper and lower parts of the skeleton in 

 the Sauropoda. All the bones above a line passing 

 through the acetabulum and glenoid cavity of the scapula 

 are very lightly constructed, and thus far Dr. Hay's 

 statement is correct. All the bones below this line are, 

 on the other hand, very massive, and solid or nearly so. 

 So far as the reviewer can judge from comparison of a 

 large series of bones, they are quite as dense and massive 

 as the corresponding bones in the hippopotamus; and 

 they certainly are not hollow in the sense that the bones 

 of Allosaurus are hollow. All of them are cancellous 

 towards the center, and in the femur there is an open 

 cavity of proportionately small size in the shaft. But 

 they are certainly far more dense than in the elephant, 

 and wholly lack the devices for lightening the weight that 

 are so conspicuous in the skull, cervical and dorsal ver- 

 tebrae, the first few caudals, the ilium and the proximal 

 ends of the ribs. The median and distal caudals, the 

 ischia, pubes and limbs, the shoulder-girdle, except for 

 the blade of the scapula, and especially the feet, must be 

 wholly excepted from Dr. Hay's statement in regard to 

 the lightening of the skeleton; they are certainly unusu- 

 ally massive in form ; and while the precise degree of den- 

 sity of the petrified bone is not very easily compared with 

 modern bone, yet in the reviewer 's opinion they compare 

 most nearly with the bones of aquatic animals, such as 

 plesiosaurs and mosasaurs among the reptiles, cetaceans, 

 pinnipeds, sirenians and hippopotami among the mam- 

 mals, and are materially exceeded in density only by the 



Dr. Hay's observations in regard to the pose of bipedal 

 dinosaurs form an interesting corollary to his views in 



: Amer. Mus. Guide Leaflet Xo. — , 1905. 



