ORGAN OF SIGHT IN MAMMALIA. 



249 



Section of the eye of a Whale. 



infundibular canal for the optic nerve, f. Outwardly the eye- 

 ball is subspherical ; but, in the section figured, the contour of 

 the cavity containing the vitreous humour, e, and lens, d, presents 

 an ellipse, with the long axis transverse : in a Balcenoptera of 65 

 feet in length, this axis measured 2^ inches, and the shorter axis 

 2 inches : the posterior curve is regular ; but, toward the cornea, 

 the sclerotic turns in quickly, c, 

 flattening the fore part of the eye : 

 the distance between the fore part 

 of the sclerotic and the bottom of 

 the eye beinor but 14 inches. In 



*/ o 



shape the cornea is a longer ellipse 

 than the eyeball, and the upper 

 border is more curved than the 

 lower : it is thinner at the centre 

 than the circumference, and is soft 

 and flaccid in the dead whale. The 

 choroid has a silvery or bluish 

 white hue on the inner surface : 

 the darker pigment is limited to 

 the ciliary processes and back of the iris. In a mysticete whale 

 ( Bal&na) the cellulosity connecting the choroid with the sclerotic 

 was of a light brown hue : the darker pigment extends from the 

 ciliary processes a little way upon the choroid : and in both kinds 

 of w r hale is so disposed as to absorb the rays of light and prevent 

 them being a second time reflected so as to disturb the spectrum 

 on the back of the retina. Of the numerous minute folds which 

 constitute the ciliary zone every third, fourth, or fifth is en- 

 larged, and produced forward to form a wrinkled corrugated 

 process about three lines long, compressed and terminating 

 obtusely : the intermediate shorter processes are of varying 

 length ; the long ciliary processes are about seventy in number, 

 in Bal&noptera. The peripheral radiated contractile fibres of the 

 iris, and the central circular ones, are conspicuous on the back 

 part of that curtain in whales : the front surface shows the wavv 

 vessels radiating from arterial canals which surround the margin 

 of the pupil which is transversely elliptical. Four equidistant 

 canals in the thick sclerotic give passage to the long ciliary 

 arteries and the vorticose veins : the two arteries which advance 

 in the direction of the long axis of the pupil terminate in a 

 canal bordering the pupil a little way from its margin : the wavy 

 branches radiate from this canal, and are prominent on the 



