468 CETACEA. 



compared with the shelving, almost concave frontal margin, to as far as the nipple- 

 like projections, and the fulness of the infero-frontal or orbito-frontal. parts are also 

 highly characteristic of the brain of Tlatanista. What is seen of the cerebellum in 

 side view, along with the several large nervous trunks, coincides in producing the 

 impression of height with vertical abruptness behind. 



The occipital facies shows great steepness, or perpendicular shelving of the 

 parietal region, and equally oblique inwardly trending borders to the lips of the 

 longitudinal fissure, with a cutting away of the post-inner occipital lobes. The 

 cerebellum is less expansive than might be anticipated, though the nerve and 

 vascular channel impressions are apt to deceive in this respect. 



JEye : its general appearance and structure. — (PL XXXVI, figs. 9 and 10.) — 

 Certainly one of the strongest peculiarities of the Gangetic dolphin (Platanista) is 

 the organ of vision. Erederick Cuvier remarks, " Les yeux sont fort petits, noirs, assez 

 profondement enchasses dans leur orbite, et situ6s a environ deux pouces au.-dessus 

 des coins de la bouche." Eschricht states that the eyes are extraordinarily small in 

 diameter, only 1^ line. It may be called a blind Whale (according to him), for the 

 perforations for the optic nerve in the skull are only rudimentary. In describing 

 the young skull I shall afterwards refer to the optic foramen, (consult PI. XL, 

 fig. 1, op). 



Fig. 17. 



A, the eye of Platanista of natural size, seen from the outside. 



B, a horizontal section through the right eyeball including orbital 

 portion of skin, &c., of natural size ; /., fatty cushion surrounding the eye; fc, 

 fibrous coat of same, with thin muscular layer below it ; m, muscular fibres ; fm, 

 fibrous membrane beneath ; s, the skin ; op, optic nerve ; c, eye-chamber ; i, iris ;. 

 iel, internal eyelid ; el, el, external eyelids ; co, cornea. 



A careful examination of the eye removed from the animal immediately after 

 death and repeated on three occasions on the eyes of different individuals, has 

 established the remarkable fact that, in this MammaKan eye, no rudiment of a 

 crystalline lens exists, although the aqueous and vitreous humours are present. 

 Moreover, in the choroid there is only a trace of pigment, and the optic nerve is 

 reduced to a thread. There is also this further imperfection, that the motor muscles 

 of the eyeball are rudimentary and form a kind of compressor of the cushion of 

 dense blubbery yellow fat, in which the eyeball is imbedded and which is immensely 

 larger than it. 



As fig. 10 shows, the upper and lower eyelids are relatively well defined, 

 and in this specimen they approach but do not meet ; the aperture being narrow, 

 about 0-20 inch in the natural condition. The cutaneous papillae of the palbebrse 

 are large; but traces of Meibomian glands or of eyelashes are not discernible. 

 Midst the fibrous fatty and connective tissues of the eyelids, bands of striated 



