22 FIELD MUSEUM OF NATURAL HISTORY 
In the third case of the scries, methods of fossilization are 
illustrated. Tlie methods shown include preservation of hard 
parts, as shells and bones, internal moulds, external moulds, 
impressions and illustrations of incrustation, carbonization, 
silicitication, phosphatization, etc. 
The fossils of the Mesozoic era represented in this hall are 
chiefly the Dinosaurs of the Jurassic period. The Jurassic dino- 
saurs were great shore reptiles; they were the largest land ani- 
mals that have ever been discovered. Among animals they are 
exceeded in bulk only by the great right-whales of modern times. 
The specimens exhibited were collected by special expeditions 
sent by the Museum for this purpose to Wyoming and Colorado. 
The central exhibit is a partial skeleton of one of the largest 
dinosaurs known. Apatosaurus. Only a little more than half of 
the skeleton is here represented. The head, neck, shoulder gir- 
dle, fore legs and the extremity of the tail are wanting entirely. 
The right hind leg below the knee is copied in plaster from other 
similar specimens. The left is modeled entirely from the right. 
The portion of the skeleton exhibited was found with all of 
its parts connected and has been carefully mounted in its natural 
position. Therefore, the body of the animal, the pelvis, the 
hind legs and the greater part of the tail are accurately repre- 
sented in their natural relations. 
The portion of the skeleton shown is thirty feet long and 
stands fifteen feet above the base. In life the neck was equal in 
length to the portion of the tail here exhibited. The tail was at 
least one half longer. From this it may be seen that the entire 
length of the animal would have been about sixty feet, or eight 
feet longer than the hall in which it is exhibited. 
The various series of vertebrae, scapulae, pelves, sacra, leg 
bones, and feet exhibited in the adjoining wall cases represent a 
number of other types of Dinosaurs, most of which are smaller 
than the central figure. Among these are represented the fol- 
lowing genera: Morosaurus, Camarasaurus, Brachiosaurus, and 
Creosaurus. 
At the end of the hall may be seen a complete fore leg and 
shoulder-blade of the medium-sized dinosaur, Alorosaurus. Two 
large leg bones of Brachiosaurus shown are the largest known to 
science. They measure six feet eight inches in length, and the 
thigh-bone weighs seven hundred pounds. The unusual 
length of the humerus in comparison with the femur shows that 
