32 



brain and its membranes. The vertical diameter of the cranial cavity is 4 inches 

 8 lines ; its transverse diameter, which is greatest at the posterior third part of the 

 cavity, corresponding with the posterior part of the cerebrum, is 6 inches. The 

 brain of the Megatherium, to judge from its bony case, must have been less, by 

 nearly one half, than that of the Elephant; but with the cerebellum relatively larger 

 and situated more posteriorly to the cerebral hemispheres : whence it may be inferred 

 that the Megatherium was a beast of less intelligence, and with the command of fewer 

 resources, or less varied instincts, than the Elephant. 



The ' maxilla superior,' or maxillary bone, may be divided into a palatal, alveolar, 

 and facial portion: the latter (Plate XII. fig. 1, 21) is remarkable for the excess 

 of its vertical over its antero-posterior extent : it forms, with the coalesced lacry- 

 mal (/), the anterior and part of the inferior boundary of the orbit by a strong sub- 

 vertical outstanding plate, curved with the convexity forward, perforated at the 

 middle part of its base by the antorbital canal (/•), which is double on the left side, and 

 near the upper part of its thick obtuse margin by the lacrymal canal (/) : it is smooth 

 behind, or next the orbit, rather rough and irregular in front : a rough, shallow de- 

 pression (Plate XIV. fig. 2, s) near the upper part of this surface indicates the origin 

 of a strong labial muscle. The outer surface of the facial plate of the maxillary is 

 smooth and slightly undulated ; it evidently extends as far as the postorbital process 

 upwards and backwards, in connexion with the nasal bone : its anterior border 

 (Plate XII. fig. 1, «), terminating the side of the nostril, is vertical, slightly concave 

 and sharp, and is smoothly excavated on the inner side or towards the nasal cavity. 

 The lower part of this nasal wall presents a deep and rough sutural notch for articu- 

 lation with the premaxillary bone. 



The alveolar part of the maxillary (Plate XV. i, v) extends about an inch below 

 the suborbital process. The extent of the alveolar tract is 10 inches ; its greatest 

 breadth is 2 inches 4 lines, viz. between the second and third teeth. The number of 

 alveoli is five. The first (?) has a subtriangular transverse section, with the apex very 

 obtusely rounded off and turned forward ; the borders of this alveolus are sharp and 

 somewhat produced below the level of the surrounding bone. The second alveolus (ii) 

 is close to the first, and the corresponding teeth are nearly in contact; its transverse 

 section is quadrate, the hinder side being the broadest, the outer side the narrowest; 

 the fore-side is more curved than the back one. The partition between this and the 

 third alveolus is thicker than the preceding one, and the teeth stand further apart. 

 The third and fourth sockets are most nearly of a square form, but the transverse 

 diameter predominates ; the fifth socket (v) is suddenly reduced in size, and re- 

 sembles most the first in form, but with the rounded apex of the triangle turned 

 backwards. 



No trace of the suture between the maxillary (21) and palatine (20) bones remains: 

 the alveolar border beyond the fifth socket (v) rapidly contracts to the thin vertical 

 pterygoid plate («). 



