Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/505

 uninjured, forms a prominent rounded angle "with the corresponding posterior (inner) border of the extremity. Here it has a width of 1 inch, which increases to 4.5 inches at the summit of the curve (the increase being chiefly caused by a swelling of the upper surface of the extremity, the terminal aspect of which is separated by a groove from the rest of the terminal surface), whence it again diminishes to 1.5 inch near the anterior (outer) missing angle. The under (anterior) surface is generally flat, with a slight longitudinal and transverse hollowing of its posterior (inner) half. The upper (posterior) surface is transversely slightly convex for 1.8 inch from its posterior (inner) border, then slightly hollow for another inch ; and from this to within a short distance of its anterior (outer) margin it is rendered strongly convex by the large subpyramidal swelling just mentioned, the base of which forms part of the terminal surface.

Distal extremity. — This is much more massive than the proximal end. Its form is somewhat cubical. The terminal surface is flatter and of an oblong figure, divided into a couple of condyles by a depression in its upper (posterior) border, and by two angular excursions of its lower (anterior) margin. The posterior (inner) condyloid surface is the larger one. The upper surface exhibits a broad, shallow, longitudinal, median groove, 5 inches wide at the edge of the terminal surface, growing narrower as it recedes from this, and dividing at about 8 inches distance from it to receive the distal end of a low median ridge prolonged from the shaft. The anterior (outer) branch of this hollow ends about 1 inch sooner than the posterior (inner) one. On the under (anterior) surface two strong subpyramidal swellings .9 inch high, corresponding to the two excursions mentioned in the lower (anterior) border of the terminal surface, and, indicating the greater projection of the condyles in this direction, immediately arrest the eye. The anterior (outer) swelling, with a base 1.8 inch wide at the terminal border, begins to rise at 1 inch from the anterior (outer or radial) border of the extremity. A deep intercondyloid notch, .8 inch wide, separates it from the posterior (inner) swelling of nearly the same size and form. Between this and the posterior (inner or ulnar) border of the extremity the surface is first longitudinally grooved by a shallow depression which has been slightly increased by compression, and then gently convex. The anterior (outer) and posterior (inner) margins are so broad and flat near the terminal border, that here they might be properly called surfaces ; but towards the shaft they grow narrower and become transversely convex.

Shaft. — Of a subcylindrical form, this comprises about the middle third of the bone. Its upper (posterior) surface is strongly convex transversely. The under surface is transversely convex in its posterior (inner) half ; but it has a shallow longitudinal median hollow, widening towards the proximal extremity, and merging into the shallow depression mentioned in the posterior half of the under surface of this. The anterior (outer) border of this longitudinal hollow rises sharply, as if it were the beginning of a deltoid crest.

Contour. — When the bone is placed horizontally the outline of the