78 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



the known difference in the position of the occipital plane, which in the Glosso- 

 there corresponds with that in the Myrmecophaga and Bradypus, we shall be 

 justified in continuing to regard them, until evidence to the contrary be obtained, 

 as belonging to distinct genera. 



The parietal bones present an oblong regular quadrate figure, the sagittal 

 suture running parallel with the squamous, and the frontal with the lambdoidal 

 suture ; there is scarcely any trace of denticulations in the sagittal suture ; the 

 bones are of remarkable thickness, varying, at this suture, from six to nine 

 lines, and their opposed surfaces are locked together by narrow ridges, which 

 slightly radiate from the low r er to the upper part of the uniting surface : the 

 substance of the bone consists of an uniform and pretty dense diploe ; and there 

 are no sinuses developed in it. We can hardly regard the extraordinary air-cells 

 which occupy the interspace of the two tables of the skull in the parietal and 

 occipital bones of the Glossothere (PI. XVI., fig. 3) as a difference depending 

 merely on age. 



The frontal and sethmoid bones are broken away in the present cranium. The 

 sphenoid commences two inches in front of the foramen occipitale ; the fractured 

 state of the skull does not allow its anterior or lateral limits to be accurately 

 defined; its body is occupied with large air-sinuses; the only part, indeed, of this 

 bone which is exposed to observation is that which forms part of the floor of the 

 cranium ; and this we shall now proceed to describe, in connexion with the other 

 peculiarities of the cranial cavity, (fig. 1. PI. XXIII.) The body of the sphenoid 

 is impressed on its cranial surface with a broad and shallow sella turcica (a), 

 bounded by two grooves, (b b 9 ) leading forwards and inwards from the carotid 

 foramina (c); the line of suture between the sphenoid and occipital bones runs 

 along a slight transverse elevation (rf), which bounds the sella posteriorly; this 

 suture is partially obliterated : a slight median protuberance (e) bounds the sella 

 turcica anteriorly ; there are neither anterior nor posterior clinoid processes. 

 External to the carotid channel there is a wide groove (f) leading to the foramen 

 ovale (g); this foramen is about one-third smaller than in the Glossothere, and 

 therefore, as compared with the anterior condyloid foramina, indicates that the 

 tongue was endowed with a greater proportion of sensitive than motive power in 

 the Scelidothere: but in reasoning on the size of this nerve, it must be remembered 

 that in both animals certain branches, both of the second and third divisions of 

 the fifth pair of nerves, are to be associated with the persistence of large dental 

 pulps, of which they regulate the secreting power. Anterior to the foramen ovale, 

 and at the termination of the same large common groove, lodging the trunk of the 

 fifth pair of nerves is the foramen rotundum (h) ; this leads to a very long canal, 

 the diameter of which is five lines, being somewhat less than that for the third 

 division of the fifth pair. The anterior sphenoid is broken away, so that no 

 observation can be made on the optic foramina. 



