394 ON A FOSSIL CALVARIA, 



I apprehend that the form and structure of the calvaria taken 

 in conjunction with the subquadrate and unsegmented outline of 

 the brain, forbid the supposition that it "was of marsupial origin. 

 A cross crestless and posteriorly sloping skull cap like this could 

 scarcely have belonged to a carnivorous placental. The type of 

 brain presented by it does not accord with that of any terrestial 

 herbivore known to the writer, who is therefore compelled to refer 

 it to some aquatic mammal. On comparing the fossil with the 

 corresponding part of the skull of the Dugong, the external 

 resemblance between the two is sufficiently obvious. The chief, 

 almost the only difference, is the still greater reduction of the 

 parietal crest, and the oblique instead of nearly perpendicular 

 descent of the bone exterior to the crest. In other words the 

 temporal fossa was shallower, the muscles working the jaws feebler 

 in the extinct than in the recent animal. On reverting to the 

 inner side of the fossil the rectangular shape of the hemispheres of 

 the brain favors, so far as it goes, the suggestion that it has 

 Sirenenian affinities. But the objections to that view are not 

 without weight. They consist in the apparent absence of the 

 fairly marked division of the cerebrum into fore and hind lobes 

 seen in both the living and extinct forms of the group — in the 

 number and symmetry of the convolutions in the presence of a 

 rudimentary tentorium, and above all in the greater proportionate 

 extent to which the cerebellum is uncovered. It is true that the 

 naked cerebellum of the Manatee figured by Dr. Murie (Trans. 

 Zool. Soc, vol. viii., pi. 25, appears to be as much exposed as that 

 of the fossil, but in a figure of the cast of the brain-case of the 

 same animal given by Professor Owen (Journ. Geol. Soc), and 

 in a similar cast of Halicore now before the writer, the proportion 

 of the cerebellum to the cerebrum, is, or seems to be much less 

 than in the extinct form under notice. Remembering however, 

 that the brains of the two surviving genera of Sirenians show that 

 considerable modifications may be consistent with the general type of 

 brain, it may not be too rash to surmise that a brain of inferior de- 

 velopment and a smoothness of skull indicatory of feebler masticating 

 power, may have been the coadaptation of the softer vegetation, 



