Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/157

Rh deltoid ridge (ib. b, b′), of similar basal extent to that in Felis, is more produced and is much thinner, extending as a broad plate of bone outward (radiad) and forward (thenad) ; it seems to be rather a development in those directions of the entire shaft than to be a superadded process of the shaft. The more rounded, thickened char- acter which prevails through nearly the whole extent of the humerus of the feline as of most mammals, is here confined to a constriction barely an inch in extent between the subsidence of the deltoid al or delto-pectoral crest and the beginning of the neuro-arterial bridge (h) on the inner side, and of the supinator crest (e) on the outer side of the lower two fifths of the bone. The perforation itself (k) is more highly placed, is further from the articular surface for the ulna, than in Felis. The ulnar articulation or " trochlea " is less defined ; the inner boundary ridge, so prominent in Felis, is here undeveloped. The convexity (fig. 6, g) for the radius, on the other hand, is relatively larger, and its ball advances further upon the fore part of the shaft, in the present fossil. In this, likewise, the anconal pit (fig. 7, d), so deep and well-defined by outer and inner ridges in Felis, is a mere wide and shallow triangular depression.

The delto-pectoral crest (b, b′) which seems to be a forward and inward production of the outer border of the proximal part of the humerus, is essentially a reptilian character of the bone. Its ordinary proportions in existing Saurians are shown in Uromastix spinipes (fig. 10, b, b′) and in Monitor niloticus ; in Crocodiles the shortening of its base gives it more the character of a distinct process; in Pterodactyles its development is chiefly in transverse extent ; in Cynodraco the longitudinal extent prevails; in Omosaurus the development in both directions of the deltopectoral crest is such as to have suggested the generic name of this Dinosaur. But the perforation or canal (h, k, fig. 6) is not present in any existing Reptile. There is, indeed, what may be loosely termed a "supracondyloid foramen" in several Reptilia. It is noticed in the osteology of the genus Trionyx; but its position in the humerus is defined:—"The bone is perforated from before backwards at the outer angle of the distal extremity". The homologous supracondyloid foramen is shown in the humerus of the Monitor niloticus, in the under-cited monograph (Note ), in pl. xvii. fig. 6, at e′, where it perforates a low supinator crest. Its position in Uromastix spinipes is shown at l′ and m in figs. 10 and 11 (Plate XI.). Dr. Günther notes the homologous foramen in the humerus of Testudo elephantopus and its allies (Testudo ephippium e.g.), and describes it as "the canal on the radial edge of the bone, close to the elbow-joint, perforating the substance of the bone from the front to the hinder side".