60 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



Glossotherium, in forming part of the circumference of an ellipse, whose long axis 

 is vertical ; and in sending outwards, from its anterior part, a convex eminence, 

 which terminates in a point directed downwards and forwards. 



Such appear to be the most characteristic features of the cranial fragment 

 under consideration, in which we have found, that the articular surface for the os 

 hyoides throws more light upon the nature of the animal of which it is a part, 

 than even the glenoid cavity itself. There now remains to be described as much 

 of the individual characters of the constituent bones as the specimen exhibits. 



The occipital bone, besides forming the posterior and part of the inferior 

 parietes of the cranium, extends for about half an inch upon the sides, where the 

 ex-occipital element is articulated by a vertical suture with the mastoid element 

 of the temporal : this suture is situated in a deep and well-marked muscular depres- 

 sion (e, fig. 1), measuring three inches in the vertical, and upwards of one inch in 

 the transverse direction. The other sutures, uniting the occipital to the adjoining 

 bones, are obliterated. The breadth of the occipital region must have exceeded 

 the height of the same by about one-third. The condyle extends nearly to the 

 external boundary of the occipital aspect of the cranium; there is situated, 

 external to it, only a small ovate, rounded and smooth protuberance. The slightly 

 concave surface of the occipital plane of the cranium is bounded above by a thick 

 obtuse ridge, the muscular impressions are well sculptured upon it. It is traversed 

 transversely at its upper third by a slightly elevated bony crest ; and the surface 

 below this ridge is again divided by a narrower intermuscular crest, which runs 

 nearly vertically, at about an inch and a half from the external boundary of the 

 occipital plane. As a similar crest must have existed on the opposite side, the 

 general character of the occipital surface in the Glossothere would resemble that 

 of the Toxodon. A similar correspondence may be noticed in the terminal 

 position of the condyle, and the slope of the occipital plane. 



Above the transverse ridge, the rough surface of the occipital plane slopes 

 forward, at a less obtuse angle with the basal plane, to the first named ridge 

 which separates the occipital from the coronal or superior surface of the skull. 

 The contour of this surface runs forwards, as far as the fragment extends, in 

 an almost straight line : the extent of surface between the temporal muscular 

 ridges must have been about five inches posteriorly, but it decreases gradually 

 as it extends forwards : all that part which is preserved is quite smooth. The 

 attachment of the fasciculi of the temporal muscle, and the convergence of their 

 fibres as they passed through the zygoma are well marked on the sculptured 

 surface of the bone. The zygomatic process is relatively stouter than in Orycte- 

 ropus: it is prismatic: the external facet is nearly plane: the superior is con- 

 cave, and increases in breadth anteriorly: the inferior surface offers a slight 

 convexity behind the flattened articular surface for the lower jaw. The margin 



