429 



wards, and fits, like a pivot, into a socket in the astragalus. The calcaneum is remarkably 

 long and compressed. The scaphoid, cuboid, and cuneiform bones have become confluent 

 with each other and the metatarsals, of which the first and fifth exist only in rudiment. The 

 other three have likewise coalesced with the proximal phalanges of the toes which they 



support. 



Presented by Samuel Stutchbury, Esq. 



2368. The skeleton of a young Three-toed Sloth (Bradypus tridactylus). 



The small pleurapophyses of the eighth and ninth cervical vertebrae have been removed. 

 Only fifteen pairs of dorsal pleurapophyses are preserved, leaving four lumbar vertebrae *. 

 There are thirteen false vertebrae, three of which articulate with the ilium, and the fifth and 

 sixth with the tuberosity of the ischium. The distal epiphysis of the ulna has not begun to 

 be ossified. 



Mus. Brookes. 



2369. The skull of a young Bradypus tridactylus. 



The interparietal has coalesced with the superoccipital, but the exoccipitals continue 

 distinct both from the superoccipital and basioccipital. The cranium is chiefly remarkable 

 for the size, shape, and connexions of the malar bone, which is freely suspended by its ante- 

 rior attachment to the maxillary and frontal, and bifurcates behind ; one division extending 

 downwards, outside the lower jaw, the other ascending above the free termination of the 

 zygomatic process of the squamosal. The premaxillary bone is single and edentulous, being 

 represented only by its palatal portion completing the maxillary arch, but not sending any 

 processes upwards to the nasals. 



Hunterian. 







2370. The skull of a Bradypus tridactylus, vertically bisected, with the teeth of the 

 left side of the upper and lower jaw separately displayed. 



There is no bony tentorium : the two divisions of the meatus internus commence sepa- 

 rately upon the exterior of the petrosal, which is not impressed by a cerebellar fossa. The 

 depression receiving the natiform protuberance of the cerebellum is formed chiefly by the 

 squamosal. The walls of the rhinencephalic fossa are entirely surrounded by the olfactory 

 chamber, which extends above into the frontal and beneath into the sphenoidal sinuses. A 

 well-marked vascular foramen leads downwards from the partition between the rhinencephalic 

 and prosencephalic chambers. The rough exterior part of the petrosal forms, as it were, the 

 border of a capsule to the tympanic : the fossa for the stylohyal is well marked at the back 

 part of the border. The pterygoid forms a large quadrate vertical plate. The bony septum 



* M. de Blainville, in noticing a similar discrepancy in the number of the dorsal vertebrae in a Sloth 

 dissected by Dr. Harlau, as compared with those observed by Cuvier, does not state whether it was 

 compensated by a proportional difference in the number of the lumbar vertebrae. 



