206 



sified an order, must be expected to be comparatively few ; those 

 which I have observed in the skull are as follows : — 



The tuberosity of the maxillary bone is articulated by the whole 

 of its upper surface to the frontal and orbitosphenoid bones. 



The zygoma is flat and straight, projecting at once outwards and 

 forwards, its articulating surface being more or less confluent with a 

 concavity at the inner side of it which forms a portion of a more or 

 less elongated cone, whose apex would point backwards. In such 

 forms as have the articulation longitudinal, the glenoid surface is 

 distinguishable from that of Rodents by its posterior termination, 

 which is not a thin free edge like the anterior. 



The alisphenoid bone never extends high, so that the pterygoid 

 ridge forms its upper boundary, or even extends above it. 



The absence of enamel in the teeth, when they exist, must also be 

 named among the cranial characters. 



Fam. 1. Bradypodid^. 



The intermaxillary bones confined to the lower part of the nasal 

 opening ; the maxillary bones provided veith simple teeth, shortened, 

 their malar processes much pushed forwards upon 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 genus 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 robustus 

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

 supratemporal process. In the Scelidotherium the process existing 



