OECELLA. 393 



The longitudinal fissure is a deep and wide cleft, with both its margins rounded ofp, 

 leaving a wide interval between the lips of the frontal and occipital corners. 

 A very considerable surface of the cerebellum is thus exposed superiorly. 



The anterior face of the brain presents a massive appearance, both breadth 

 and depth being conspicuous. The supra-orbital region is specially prominent. 

 What corresponds to the optic nerve tract presents a moderately marked vertical 

 ridging situate about the middle. This front surface of the brain is relatively 

 truncate and flattish as a whole. 



The profile or lateral aspect (fig. 5) of this brain mould shows, not only the 

 cerebellar exposure, but that the cerebellum is of a good height, and that the 

 cerebrum is much deeper in the frontal than in the occipital region. The outline 

 of the cerebral hemisphere from this point of view is kidney-shaped, the infra- 

 orbital region fullest, and the Sylvian fissure shallow and only noticeable low down. 

 A rim of projection at the margin of the post infra-occipital sweep, and a semilunar 

 ridge facing this, on the surface of the cerebellum, mark the depressions excavated 

 in the bone for the large venous sinuses. The root of one of the branches of the 

 5th nerve stands well out, and the elevation of the orbital nerve (as alluded to 

 on the anterior face) crops forward beyond the supra-frontal margin. If a vertical 

 line be drawn giving the extreme limit of height of the cerebrum (which is in 

 front of the Sylvian fissure), and another horizontally at right angles to this 

 giving the extreme length of the cerebral hemisphere, these would show but a 

 slight preponderance in favour of the latter. In other words, depth and breadth 

 are characteristic features of this brain, but the latter, as shall hereafter be 

 shown, is the distinguishing and most obvious difference between it and that of 

 Platanista. The figures in Plate XXX, however, do not afford a fair comparison, 

 as those of P. gangetica are representations of the brain itself, whilst those of 

 Orcella are from the mould of the cranial cavity. 



As in the upper surface, the base of the brain (fig. 6) is of great breadth^ 

 and the cerebellum is seen to cover a considerable area. TMs surface, moreover, 

 taken as a whole, is remarkably flat, but especially so in the extensive figure-of- 

 eight boundary formed by the infra-orbital regions, pons and cerebellum. A raised 

 median, transversely oval portion, possibly iadicative of a good-sized flocculus, is 

 noticeable on each half of the cerebellum. 



With regard to the nervous trunks, their great thickness, so far as this cast 

 is concerned, is apparent rather than real, inasmuch as they give the capacity 

 of the foramina and basi-cranial grooves ; for, as is well known in Cetacea, the 

 nerves are accompanied by accessory vascular plexuses and thick sheaths giving 

 increment of bulk other than what is due to the nervous cords themselves. It 

 may be remarked, however, that the 5th, 6th, 7th, and 8th pairs possess a magni- 

 tude corresponding to the functional importance of these nerves in the whale 

 group. 



Viewed from behind, the brain cast displays the occipital borders of the cere- 

 brum obliquely pitched, and covering and overlapping outwardly the cerebellum, 



b3 



