During ten years explorations in the Western Cretaceous formations, Mr. Brown has secured for the Museum three skeletons of this magnificent dinosaur, incomplete, but finely preserved. The first, found in 1900, included the jaws, a large part of backbone and ribs, and some limb bones. The second included most of skull and jaws, backbone, ribs and pelvis and the hind limbs and feet, but not tail. The third consisted of a perfect skull and jaws, the backbone, ribs, pelvis and nearly all of the tail, but no limbs. From these three specimens it has been possible to reconstruct the entire skeleton. The exact construction of the fore feet is the only doubtful part. The fore-limb is very small relatively to the huge size of the animal, but probably was constructed much as in the _Allosaurus_ with two or three large curved claws, the inner claw opposing the others. [Illustration: Fig. 14.--Quarry from which the _Tyrannosaurus_ skeleton was taken. American Museum camp in foreground.] The missing parts of the two best skeletons have been restored, and with the help of two small models of the skeleton, a group has been made ready for mounting as the central piece of the proposed Cretaceous Dinosaur Hall. One of the skeletons is temporarily placed in the centre of the Quaternary Hall, space for it in the present Dinosaur Hall being lacking. Following is Professor Osborn's description of the preparation of this group:[9] "The mounting of these two skeletons presents mechanical problems of very great difficulty. The size and weight of the various parts are enormous. The height of the head in the standing position reaches from 18 to 20 feet above the ground; the knee joint alone reaches 6 feet above the ground. All the bones are massive; the pelvis, femur and skull are extremely heavy. Experience with _Brontosaurus_ and with other large dinosaurs proves that it is impossible to design a metallic frame in the right pose in advance of assembling the parts. Even a scale restoration model of the animal as a whole does not obviate the difficulty. "Accordingly in preparing to mount _Tyrannosaurus_ for exhibition a new method has been adopted, namely, to _prepare a scale model of every bone in the skeleton_ and mount this small skeleton with flexible joints and parts so that all studies and experiments as to pose can be made with the models.