431 



2379. The right ulna, longitudinally bisected, showing the absence of a medullary 

 cavity : the distal epiphysis is long and is still ununited. 



2380. The right radius, longitudinally bisected, showing the absence of a medullary 

 cavity, and the epiphysial sutures at both extremities. 



2381. The carpus and metacarpus of the right fore-foot. 



The carpus is reduced to six bones, the scaphoid being connate with the trapezium, and 

 the magnum with the trapezoides. A rudiment of the metacarpal of the pollex has coalesced 

 with that of the index, and a rudiment of the metacarpus of the minimus with that of the 

 annularis, but a trace of the original separation remains. 



2382. The ungual phalanges and the claws of the same fore-foot. 



2383. The right tibia, longitudinally bisected, showing the rudiment of a medullary 

 cavity, towards which the minute arterial canal is directed. The epiphyses 

 are still ununited at both ends of the bone. 



I 



2384. The right fibula, longitudinally bisected, showing the absence of a medullary 

 cavity, and the large size of the lower epiphysis. 



2385. The tarsus and metatarsus of the left hind-foot. 



The ento- and meso-cnneiform bones, the rudimental metatarsal of the hallux, and the 

 metatarsal of the second toe are confluent into one bone : the rudimental metatarsal of the 

 fifth toe has not become united with that of the fourth toe. 



2386. The ungual phalanges and claws of the same hind-foot. 



2387. The skeleton of the Two-toed Sloth (Cholcepus didactyltis). 



The vertebral formula is : 7 cervical, 23 dorsal, 3 lumbar, 8 sacral, 4 caudal. The cla- 

 vicles are entire : the large coracoid is still ununited with the scapula : the humerus is per- 

 forated above the inner condyle. The functional digits of the fore-foot are reduced, as in the 

 Ruminants, to the third and fourth, with a rudiment of the metatarsal of the second and of 

 the fifth toes. The skeleton is of a young animal. The elements of the occipital bone are 

 still ununited. The tympanic cells extend into the base of the zygomatic process, which ter- 

 minates freely forwards and does not join the broad bifurcate malar. The lacrymal is pierced 



