PEOFESSOE OWEN ON THE SCELIDOTHEEE. 
105 
nearly con-esponds with that of the tooth it contains. The maxillary extends 4^ inches 
in advance of the first alveolus, in an obtusely pointed form, slightly diverging from its 
fellow to form the hinder two-thirds of an unusually long prepalatine or incisive fissure 
(i). The side of the fore-part of the maxillary is deeply notched for a corresponding 
process of the premaxillary ( 22 '). The upper surface of the palatine plate is longitudinally 
grooved, and the inner border of the groove unites with its fellow to form a median ridge. 
The premaxillaries ( 22 ) have partially coalesced anteriorly, where each forms an obtuse, 
rounded, subcompressed protuberance, expanding as it passes backwards and bifurcating. 
The inner branch, 3 inches in length, uniting with its fellow, forms a long and slender 
trihedral process, diriding the prepalatine fissm'e, at its upper part, into two : the ridged 
summit of this process is grooved at its fore-part. The outer process of the premaxillary ( 22 '), 
which answers to its ascending branch [tranche montante of Cuvier) in ordinary mammals, 
forms the horizontal lower part of the boundary of the external bony nostril, and termi- 
nates obtusely a little behind the angle between that part and the vertical part of the 
boundaiy, filling up the before-mentioned maxillary notch : the length of this process is 
inches. The enthe length of the premaxillary is 4|- inches : the obtuse anterior ends 
of the premaxillaries are partially separated by a notch. 
The relative size, shape and connexions of the lacrymal bone are better defined in one 
of the crania of the Scelidothere in the British Museum than in any other Megatherioid 
fossil which has hitherto come imder my inspection ; this bone (Plate VIII. figs. I & 2, 73) 
forms the anterior two-thhds of the upper boundary of the orbit, where it is wedged 
between the maxillary and the frontal, articulating by about half an inch of the upper 
border with the nasal bone, and for about the same extent by its anterior and inferior 
angle mth the malar : it is semioval in shape, irregularly convex externally, and per- 
forated near its anterior border obhquely by the lacrymal canal [1), the orifice of which 
is 6 lines in diameter. The bone forms a slight protuberance behind the orifice, which 
appears to be outside the upper and fore part of the orbit. The breadth of the 
lacrymal bone is 2 inches. The size of the lacrymal foramen equals that in the 
Megathere, and is twice the size of that in the Mylodon : in its extraorbital position it 
difiers from both. The lacrymal canal is continued inward and fonvard, and then grooves 
obliquely the inner side of the facial plate of the maxillary, as above described. The 
secretion of the gland may finally have entered the fore-part of the mouth by the pre- 
maxillary fissure. 
The malar (Plate VIII. fig. 1, 25 ) presents the characteristic form and development of 
that bone in the Sloth tribe, with the same absence of the postorbital process as in 
the Mylodon, and a suppression of the zygomatic process (z) to a degree which brings 
it nearly to the condition of the malar in the existing Sloths. The fore part of the 
malar ( 26 ) forms the fore part of the orbit, articulating by its upper errd rrith the lacrymal 
(73), and by its fore surfiace rvith the outstanding malar process of the maxillary (21'). 
Becoming free, the malar forms a stem with a semi-elliptic transverse section, slightly 
convex externally, very convex inter-nally, 9 hrres in diameter: it then, extending 
