On the affinities of the Stereognathus ooliticus (Charlesworth) : a mammal from the oolitic slate of Stonesfield / by Professor Owen.

  • Owen, Richard, Sir, 1804-1892.
Date:
1857
Catalogue details

Licence: Public Domain Mark

Credit: On the affinities of the Stereognathus ooliticus (Charlesworth) : a mammal from the oolitic slate of Stonesfield / by Professor Owen. 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.

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    of a left ramus ; the slight inclination of the cusps of the teeth (figs. 1, 3, & 4) towards the end a, might be deemed evidence of its belonging to the right ramus : but neither this degree of inclination, nor tbe position of the accessory cusp, fig. 3 a, are decisive of the way in which the fore end of the fragment points*. Not more of the matrix can be safely meddled with, on the small chance of more evidence to this comparatively unimportant point being had; and I shall, therefore, proceed with the description of the fossil on the assumption that the shallower end, a, is the front end, the deeper one, b, the hind end of the fragment, and that it is part of the left ramus of the mandible. This ramus is unusually shallow, and broad or thick below, the side passing by a strong convex curve into the lower part; a very narrow longitudinal ridge, continued after its subsidence by a few fine lines, forms a tract which divides the lateral from the under surface : elsewhere the bone is smooth, without conspicuous vascular perforations. The depth or vertical diameter of the ramus is not more than two lines. This portion of jaw contains three teeth, the middle one of which is the least mutilated ; and by carefully removing the matrix which partly covered its crown, I exposed the whole of its singularly mo- dified grinding surface. The first of the three teeth (figs. 1 & 2, a) appears to have been smaller than the others, but its crown has been too much broken to show its original characters. The third tooth, c, is less mutilated : it is of the same size and had the same structure as the middle one, b. Of this, the most perfectly preserved of the three, b, careful drawings have been made, magnified about 8 dia- meters, figs. 3, 4 & 5. The crown of this tooth is of a quadrate form, 3 millimeters by 2,\ millimeters, of very little height, and supports six subequal cusps, in three pairs, each pair being more closely connected in the antero- posterior direction of the tooth than transversely. The outer side of the crown (fig. 3), supported by a narrow fang which contracts as it sinks into the socket, shows two principal cusps or cones, o, d, and a small (anterior) accessory basal cusp, a. A small portion of the outer side of the anterior cone, o, has been chipped off; that of the second cone, o', shows a well-marked con- vexity. The hard and shining enamel which covers these parts of the crown contrasts with the lighter cement that coats the root, fig. 3, r. The two outer lobes or cones are subcompressed, and placed obliquely on the crown, so that the hinder one, d (fig. 5), is a little overlapped externally by the front one, o, the fore part of the base of the hinder one being prolonged inwards on the inner side of the base of the front cone. The two middle cones (fig. 5, h, i) are sub- compressed laterally, with the fore part of their base a little broader than the back part. The two inner cones, p, p', have their inner surface (fig. 4) convex, with their summits slightly inclined forwards : a small portion of enamel has been chipped off the hinder lobe, p'. * Compare the tooth, m 2, fig. 2 (Hyopotamus), Plate VIII., ' Quart. Journ. Geol. Soc.'vol. iv. 1848.