On the distal end of a mammalian humerus from Tonbridge (Hemiomus major) / by H.G. Seeley.
- Harry Govier Seeley
- Date:
- 1899
Licence: Public Domain Mark
Credit: On the distal end of a mammalian humerus from Tonbridge (Hemiomus major) / by H.G. Seeley. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
5/6 page 415
![Yol_ 5^.] OF A MAMMALIAN HUMERUS FROM TONBRIDGE. 415 depression. Above the condyles in front there is the usual supra- condylar depression, somewhat deep and narrow. On the posterior aspect the distal end shows its moat distinctive features. A long narrow olecranon-pit extends above the small external condylar surface. It is ovate in outline, filled with limonite, is inch long and fully | inch wide in the middle. The inner bord'er is comparatively straight and vertical, and the outer border is convex. The small external condylar surface below the olecranon-pit is an inconspicuous convexity about ^ inch deep. No part of the inner condyle is visible on the posterior aspect of the bone. The bone which margins the upper half of the olecranon-pit on the inner side is inch wide, rounded from side to side, but slightly worn. The external margin of the pit, which may also be a little worn, is about half as wide. This character of the relatively external position of the olecranon-pit is seen in the humerus of the tapir, and to some extent among horses. The lower half of the process which usually borders the olecranon- pit is absent in this fossil; and on the inner side, in its place, is an ovate cartilaginous surface, concave in length, inclined obliquely inward, making an angle of about 45° with the axis of the shaft. There is a similar, but much smaller, atrophy of the corresponding process on the external side, giving rise to a truncated surface, | inch deep, forming a narrow crescentic impressed area. This character defines a lateral concavity between the hinder end of the humerus and the anterior border of the olecranon-process of the ulna. This truncation of these parts of the humerus is especially common in antelopes and deer; but, in comparison with known types, recent and fossil, it is much more developed in the Tonbridge fossil animal. There is no Tertiary mammal in which the character is so conspicuous as in existing types. If Hyracoiherium or Plio- lophus has the distal end of the bone placed as far forward on the shaft, it entirely wants the truncation of the bone on the lower borders of the olecranon-pit; and there is no other fossil genus with which the specimen has a closer affinity. This consideration is perhaps evidence against the fossil being derived from some Tertiary stratum and accidentally left where it was found, and so far is favourable to the specimen being of Wealden age. On the whole, the weight of evidence from comparison with other types appears to incline towards reference of the fossil to the Artio- dactyla, though there are almost a.s many points in common with the Perissodactylate humerus. In neither is the hinder part of the distal articulation of the bone comparable to this fossil. I therefore infer that it indicates a new family type. The teeth described by Mr. Smith Woodward and by Mr. Lydekker are indicative of much smaller mammals from the Wealden Beds, and the interest of the specimen now described is chiefiy in its size. It may be known as Hemiomus major, gen. et sp. nov., in reference to the absence of ossification of the hinder aspect of the distal end of the bone, and as indicative of its size.](https://iiif.wellcomecollection.org/image/b22412840_0007.jp2/full/800%2C/0/default.jpg)
