28 



element forms nearly the whole posterior region of the skull* ; and guided by 

 the remains of the suture joining it with the squamo-temporal, and by the 

 analogy of the young Scehdotheref, it probably encroached upon the coronal 

 surface of the skull and joined the parietals by a transverse lambdoidal suture. 

 This broad supra-occipital plate is, upon the whole, slightly convex, and 

 inclined from below upwards and forwards ; developing superiorly the occi- 

 pital crest, the strongest in the whole cranium of the Mylodon, and a little below 

 this, on each side, a narrower and sharper ridge (e) receding from the upper 

 crest as it curves downwards towards the condyle, and leaving a deep concavity 

 in the interspace. Immediately above each condyle there is a small foramen. 

 A groove runs down from this foramen to the inner side of the condyle, widening 

 as it descends : the middle of the upper part of the foramen magnum presents a 

 wide but not deep emargination. 



The extent of the parietal bones was doubtless great, but cannot be precisely de- 

 fined in the present cranium : their outer plate is almost flat and smooth above, 

 and is bent down at nearly a right angle upon the side of the temporal fossa ; the 

 extent of this descending plate, and the straight course of the squamous suture 

 is indicated by the depression containing its nearly obliterated remains J. 



The squamo-temporal plate and its zygomatic process have been already de- 

 scribed, and the detached condition of the tympanic bone has been alluded to ; the 

 petrous and mastoid elements are confluent, but the sutures dividing the latter 

 from the squamous and from the supra- and ex-occipitals are distinct. Nearly the 

 whole of the stylo-hyal (6) and digastric (c) cavities are formed by the mastoid bone. 



The anterior extent of the frontals is shown by the persistent fronto-maxillary 

 suture on the left side ^ ; elsewhere these bones are confluent with each other, 

 with the parietal, with the sphenoid, and even with the broad nasal bones. 

 The nasals have likewise coalesced, except near their expanded anterior extre- 

 mities, where a trace of the median harmonia remains. 



The fronto-maxillary suture, which is unobliterated on the right side, and the 

 malo-maxillary suture, define the proportions in which the frontal, maxillary and 

 malar bones respectively enter into the formation of the frame of the orbit. 



The cranial division of the skull seems, on an outward inspection, to be of 



* Plate V. fig. 1. t Zoology of the Beagle, Fossil Mammalia, p. 77. pi. 22. 



I This depression is well shown in Plate II. § Plate III. 



