350 Zoological Society. 



their malar processes much pushed forwards upou them, and the 

 molar series converging behind ; the posterior palatine foramina re- 

 placed by a series of minute openings extending the whole length of 

 the palate ; the malar bone having a descending masseteric process 

 transversely compressed, longitudinally extended, and with a di- 

 stinct superadded process arising between its frontal and zygomatic 

 processes ; the foramen rotundum distinct, and opening exteriorly at 

 the base of the pterygoid process some distance below the spheno- 

 orbital foramen and anterior to the foramen ovale ; the zygoma 

 straight and trigonal, its origin thick and extensive, reaching back 

 quite to the posterior part of the squamous bone ; the mastoid bone 

 with a wide digastric fossa, and a strong thick styloid process, ter- 

 minating in a circular concavity for the reception of the stylohyal 

 bone ; the lower jaw widened anteriorly with an extended symphysis. 



It must be observed that the superadded process of the malar bone 

 is peculiarly characteristic of this family, and is quite distinct from 

 any of the processes of that bone to which special names have been 

 assigned. It is situated between the frontal or postorbital and zygo- 

 matic processes, both of which seem also to exist in a more or less 

 rudimental form in most of the known species ; and when the latter 

 is wanting as in the geims Choloepus, the fact that the new process 

 stands aloof, above the zygoma, is enough to prevent its being taken 

 for the zygomatic process, which in all mammalia possessing a com- 

 plete zygomatic arch either abuts simply against the extremity of the 

 zygoma, or more generally seems to support it from beneath. 



The zygomatic process is well developed in the Megatherium, and 

 completes the arch, leaving the other, which might be called the 

 supratemporal process, projecting above it. In Mylodon robiistus 

 the frontal process is reduced to a slight angle upon the base of the 

 supratemporal process. In the Scelidotherium the ))rocess existing 

 above the zygomatic process appears to be broken off, but the obli- 

 quity of its base renders it improbable that it would be the true 

 frontal process so largely developed. 



The circular pit for the attachment of the stylohyal bone is pre- 

 cisely similar in the Sloths to that in the large fossil genera, and it 

 is somewhat remarkable that Prof. Owen, while describing the cha- 

 racter in these extinct forms, should have made no allusion to its 

 existence in the recent Sloths, even though Cuvier expressly points it 

 out. The tongue is largely developed in this family, and the living 

 sloth may be seen to make great use of it in taking food into its 

 mouth, as was observed by Mr. Ball, in a short communication pub- 

 lished in the ' Proceedings' some years back. On the other hand, it 

 is long and slender in the insect-feeding tribes, so that the maximum 

 degree to which it was developed in the Glossotherinm is certainly 

 no indication that such was the food of that remarkable genus. 



Cholcepus, Illiger. 



Intermaxillary bones small, produced anteriorly ; postorbital pro- 

 cess well-developed ; malar bone with a well-marked frontal process, 

 but no zygomatic process, the supratemporal process projecting 



