828 PROFESSOR DAVID HEPBURN ON 
in its fronto-occipital diameter ; 115 mm. in its greatest transverse diameter at a point 
well forward on the temporo-sphenoidal lobes; and 71 mm. in vertical height, measured 
from the pons varolii to the vertex of the cerebrum. Thus, apart from the peculiarity 
of its general outline in total size, it was only slightly less than an average human brain. 
Throughout the anterior two-thirds of their extent the cerebral hemispheres were, as 
already indicated, in very close apposition, and the falx cerebri only dipped into the 
pallial or superior longitudinal fissure to a slight extent; but in its posterior third this 
cleft opened to form a wide interval, measuring 65 mm. in the transverse direction at 
its hinder end and narrowing as it ran forwards towards the posterior end of the corpus 
callosum. In the deep level of this interval the pineal body and the upper surface of 
the vermis were visible, as well as part of the upper surface of the cerebellar hemispheres. 
It should be stated that the backward extension of the occipital lobes of the cerebrum 
carried them 2 mm. beyond the cerebellar hemispheres. 
In its essential features the basal aspect of the brain conformed to current 
descriptions of the mammalian brain ; but it presented many special points of interest, to 
which reference will be made in the course of my survey. 
J. CEREBRAL CONVOLUTIONS AND FISSURES. 
Regarded as a whole, the cerebral convolutions (gyri) were large and well defined 
from each other by deep, well-marked fissures (sulci), and yet many furrows not deep 
enough to be regarded as sulci were seen crossing the surfaces of convolutions. In- 
variably these shallow furrows were in the position of blood-vessels ramifying in the pia 
mater, and it was clearly demonstrable that the furrows were produced by the blood- 
vessels. In appearance they resembled the arterial grooves upon bony surfaces, and 
their presence upon the surface of the brain suggested either arterial pulsation or resist- 
ance to brain growth as their determining cause. Indeed, from the distinct character of 
many of them it would not be difficult to credit these vessels with the possibility of 
determining the position of new fissures in a rapidly expanding hemisphere. In their 
chief and outstanding characters the two hemispheres corresponded with each other ; 
but in the matter of intimate detail they presented a considerable amount of asymmetry, 
although neither hemisphere could be said to be more elaborately convoluted than the 
other. 
The general plan of the convolutions and fissures was not simple or easy to determine. 
In fact, the whole arrangement bore very little if any resemblance to that presented by 
the brain of a typical member of the carnivora, e.g. the dog; and this is somewhat 
remarkable and unexpected when we remember that the seals are themselves carnivores 
notwithstanding their numerous adaptations to an aquatic habitat. Partly for this 
reason, and partly because my observations do not altogether harmonise with those of 
Moritz” in his description of another seal (Otarza jubata, the sea-lion), nor with those 
* Mortis, Z’runs. Zool. Soc. Lond., vol. viti., 1874. 
