■ li. 8. Lull — Stegosaurus ungulaUis Marsh. 367 



The great power of tlie fore limbs is at once evident fi-om 

 the size of the scapular arch, the immense rugosities of the 

 humerus and the development of the olecranon process imply- 

 ing a somewhat hent, easily flexed limb excelled only by the 

 huge-headed dinosaur Triceratojys. 



The hind limbs, on the contrary, while powerful, were pillar- 

 like, as the straight shaft and character of the knee joint give 

 positive evidence. The fourth trochanter of the femur, so 

 prominent in bipedal dinosaurs, is lacking, though the origin 

 of the caudo-femoral muscle is nevertheless distinctly indi- 

 cated. The loss of this trochanter together with the slight 

 development of the pubic peduncle of the ilium precludes the 

 possibility of a bipedal gait, though doubtless Stegosaurus is 

 derived from a bipedal ancestry, quadrupedalism being secon- 

 darily acquired as in the Ceratopsia, owing to the immense 

 weight of the creature's armament. 



The vertebrae are unique in the curious upward prolonga- 

 tion of the neural arch and spine, the transverse processes and 

 zygapophyses being borne high upon the latter, thus producing 

 not only a very rigid back when subject to vertical strains but 

 also raising the ribs and thus increasing the lung and visceral 

 capacity of the body very materially without adding to its 

 breadth. The whole character of the vertebrge and ribs, the 

 latter being T-shaped in cross section near their proximal end, 

 thus giving great stiffness and a broad bearing surface with 

 the minimum of weight, is a wonderful adaptation for bearing 

 the great dermal plates with which the back was adorned. 



The feet are large as though to support the creature's weight 

 on yielding soil, the hand evidently possessing five, while the 

 foot bore three, well-developed digits. The semi-digitigrade 

 feet were doubtless enclosed in a fleshy mass as in the modei'n 

 elephants, while the external indications of the digits were 

 mainly the hoof-like nails. 



The body is extremely lank and the hips narrow, the breadth 

 across the deltoid crests of the humeri being the greatest 

 diameter of the animal's frame. 



The dentition in common with that of other predentate 

 dinosaurs, except HypsilopJiodon., is confined to the rear por- 

 tion of the jaws, the anterior part of the mouth being entirely 

 toothless, very small, and probably ensheathed in a horny crop- 

 ping beak. The dental battery, while of the same general type 

 as that of Campiosaicrics or Iguanodon, is very imperfectly 

 developed, as the teeth are small, weak structures with crenu- 

 lated margins and entirely invisible from the outside of the 

 skull and jaws when closed, implying a food of a very yielding 

 character which did not require the forcible mastication of 

 that of Iguanodon or more especially of the late Cretaceous 



