520 DE. J. MUEIE ON THE ANATOMY OF THE SEA-LION. 



each hemisphere exactly corresponds to the breadth of both, taken at the hinder half of 

 the brain. And although the frontal half is, as shown, somewhat narrower, yet the 

 above measurements bring out what is the impression at first sight conveyed to the eye 

 — namely, that the brain altogether approximates to an equal-sided figure. 



The lateral aspects are as remarkable as the superior one, and more clearly demon- 

 strate the infracerebral position of the cerebellum. In this view the entire brain 

 possesses somewhat of an oval shape, the anterior portion of the frontal cerebral lobe 

 narrowing rather angularly, while the rounded, bulbous olfactory surface projects 

 beyond ; and together they have considerable vertical depth. Each occipital lobe 

 tapers backwards with a semicircular outline, the inferior border being the straighter 

 of the two. The temporal lobe is broad, tolerably vertical, or only inclined moderately 

 forward ; in front of it a wide and deep depression exists, the Sylvian fissure with its 

 marginal convolution. As in the upper view, the hemispherical segment behind 

 the aforesaid depression or constriction is seen, when viewed sideways, to be decidedly 

 convex, the most protuberant point being the upper part of the temporal lobe ; but on 

 the contrary the anterior or frontal segment is remarkably flat and perpendicular. A 

 vacuity corresponding to the osseous elevation of the periotic occurs behind the temporal 

 lobe and cerebellum, partially exposing the pons Varolii. 



The contour of the base of the brain agrees pretty well with its upper surface, The 

 olfactory lobes are broadish and bulbous in front, narrower at their middles, and widen 

 and flatten behind, as they divide in an arched manner into the short inner and longer 

 external roots. The anterior segment, or orbital region, is flat. 



The Sylvian fissures are deep; and behind them the temporal lobes form a well- 

 marked arch, the keystone of which is the roots of the optic nerves. The optic com- 

 missure is large and long, the nerves not separating from their single investing sheath 

 till they arrive at the foramen opticum. 



The accompanying table represents a series of measurements of the Cerebrum and 

 Cerebellum, corrected by the intracranial cast, with the ratios of the same. They cor- 

 respond to what obtains in the (European) human brain, taking the latter as a standard 

 of comparison in units — namely that given by Marshall, Phil. Trans, p. 554. I reserve 

 comparisons and other remarks on the brain of the Pinnipedia for a future occasion, 

 restricting this part of my researches to anatomical description. 



Cerebrum. 



(Otaria jubata 6 .) 



Dimensions in inches. Eatio. 



«. Greatest breadth (viz. at the temporo-occipital lobes) 4'0 0-58 



b. Ditto length, antero-posteriorly 3-8 0-80 



c. Ditto height ditto ditto . 2-9 0-64 



d. Length (or oblique height) of the orbital surface . 1-4 0-60 



