1903.] 



The Brain of the Archceoceti. 



323 



several peculiarities of the natural cast — such, for example, as the form 

 of the caudal part of the cerebellum and the shape of the cerebral 

 hemispheres — which are difficult to reconcile with the artificial mould, 

 even if we admit that the inner face of the cranium (from which the 

 latter was made) is damaged or imperfectly cleaned. The differences, 

 nevertheless, are sufficiently pronounced to indicate a generic dis- 

 tinction between the two specimens; and in this connection it is 

 interesting to recall a statement made by Dr. Andrews in his first 

 reference to Zeuglodon, as " including apparently Dames' Z. Osiris, and 

 perhaps a second species."* It would, however, be very unwise, 

 because it would serve no useful purpose, and possibly lead to error, 

 to found a new genus or even a new species on the evidence of this 

 natural cranial cast, when our source of information concerning the 

 known genus (Zeuglodon) is as unsatisfactory as that obtainable from 

 the artificial one about to be described. More especially so, when it is 

 remembered that in the case of the only indisputable facts (i.e., size 

 and general form) the two casts are agreed. I shall therefore merely 

 describe and attempt to explain the meaning of the form of the two 

 specimens, and leave the question of the specific identity open for 

 future research. 



The general appearance of the brain is extraordinarily peculiar 

 (figs. 1 and 2). The shape of the anterior part of the natural cast 

 (fig. 1, a and b) closely resembles the cerebrum of a Lizard greatly 

 magnified. An anterior prismatic stalk (a), representing the pedunculi 

 olfactorii, suddenly expands into a plump, broad, smooth mass (b), 

 showing the form of the chief part of the cerebrum. The maximum 

 breadth of the two hemispheres (fig. 1, b) is 95 mm.; the greatest 

 length of each (measured in front from the point where the ventral 

 surface of the olfactory peduncles appear to expand into the chief mass 

 of the hemisphere) is 47 mm. ; and the maximum depth is 54 mm. 

 Each cerebral hemisphere (exclusive of the olfactory peduncle) is 

 slightly broader than it is long. 



The two olfactory peduncles are represented in the natural cast by 

 a single prismatic process. This extends forward for a distance of 

 37 mm. (measured along the dorsal edge) in front of the point where 

 the expansion to form the hemispheres commences; and as the 

 peduncles are broken across there, it is not possible to estimate their 

 total length or the shape and size of the olfactory bulbs. 



The coronal section formed by its anterior (broken) surface gives 

 an isosceles triangle with a base measuring 8*5 mm. and sides of 

 10 mm. each. It expands as it passes backward, so that at its junc- 

 tion with the rest of the hemisphere its sides are each 19 mm. and its 

 base 16 mm. in length. 



In the artificial cast (fig. 2) all that represents this extensive 

 # 1 Geological Magazine,' September, 1901, p. 401. 



