DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 519 
the superficies, especially at its hinder portion. The venous sinuses are prominent, and 
fit into the remarkably deep grooves already mentioned in the description of the interior 
of the cranium. ‘There is a considerable thickening of the dura mater as it passes out 
of the foramen magnum backwards towards the spinal canal. Vascularity also distin- 
guishes the pia mater, otherwise of an ordinary character. 
3. The Brain. 
a. Its outward aspects and dimensions.—The general characteristic feature of the 
brain of Ofaria, looked at on its upper surface, is its comparative squareness—in this 
respect differing from the more common ovoid form of mammals generally, as well as 
from the somewhat circular contour which it assumes in Phoca and particularly in 
Cetaceans. This quadrilateral configuration is chiefly produced by the abrupt trun- 
cation of the frontal and occipital lobes respectively, their outer corners being con- 
siderably angular, or but very moderately rounded. ‘The lateral margins are deeply 
indented about their middles; and the fronto-parietal portions are less prominent than 
the temporo-occipital ones; nevertheless they, on the whole, still lend something to 
the general quadrilinear aspect of the entire encephalon. Notwithstanding what has 
been said, each cerebral hemisphere superiorly presents a reniform outline, the deeply 
indented Sylvian fissure being equivalent to the hilus, and the straight-edged longi- 
tudinal fissure to the dorsum. The olfactory bulbs are large, and mesially project 
considerably forwards. The posterior lobes of the cerebrum are tolerably equal in 
dimensions: the left may be slightly longer than the right; but this was not clearly 
appreciable by measurement, though appearing so to the eye. 
Unlike some of the so-called higher forms of Carnivora, the posterior cerebral lobes — 
all but overlap the cerebellum laterally, as Huxley has recorded is also the case in 
the allied genus Trichechus. The actual amount of backward projection of the outer 
cerebellar lobes is little more than 0-1 inch. Mesially, however, the superior vermi- 
form and superior posterior lobes of the cerebellum are more exposed, have a 
_triangular form 1:1 inch long and 1:3 inch broad, and reach slightly further back than 
the external lobes. 
The cerebral convolutions are numerous and well developed, giving this upper sur- 
face quite a sinuous appearance. There is a certain amount of asymmetry between the 
halves; but this shall be described hereafter. The brain is highest behind, or at the 
junction of the occipital with the parietal lobes; and from this it inclines downwards 
and forwards, as also more steeply outwards. 
Measured from the anterior extremity of the olfactory lobe backwards in a straight line 
to the most projecting part of the cerebellum, the total length is 4:6 inches. The dia- 
meter across the parietal lobes is 3°2 inches. The extreme longitudinal axis of each 
moiety of the cerebrum is 4inches. The greatest transverse diameter of the brain, which 
is about the middle of the occipital lobes, is also about 4 inches. Thus the length of 
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