34(5 PHILOSOPHICAL TRANSACTIONS. [anNO 1787. 



outwards they become broad, may in some be divided into 4, and are inserted 

 into the sclerotic coat, almost all round the eye, rather behind its transverse 

 axis. 



The two oblique muscles are very long; they pass through the muscles of the 

 eyelids, are continued on to the globe of the eye, between the 2 sets of straight 

 muscles, and at their insertions are very broad; a circumstance which gives great 

 variation to the motion of the eye. The sclerotic coat gives shape to the eye, 

 both externally and internally, as in pther animals; but the external shape and 

 that of the internal cavity are very dissimilar, arising from the great difference 

 in the thickness of this coat in different parts. The external figure is round, 

 except that it is a little flattened forwards; but that of the' cavity is far otherwise, 

 being made up of sections of various circles, being a little lengthened from the 

 inner side to the outer, a transverse section making a short ellipsis. In the 

 piked whale the long axis is 2 and -| inches, the short axis 2 and ^ inches. 



The posterior part of the cavity is a tolerably regular curve, answering to the 

 difference in the 2 axes; but forwards, near the cornea, the sclerotic coat turns 

 quickly in, to meet the cornea, which makes this part of the cavity extremely 

 flat, and renders the distance between the anterior part of the sclerotic coat and 

 the bottom of the eye not above an inch and a quarter. In the piked whale the 

 sclerotic coat, at its posterior part, is very thick: near the extreme of the short 

 axis it was ■^ an inch, and at the long axis J-th of an inch thick. In the 

 bottle-nose whale, the extreme of the short axis was 4. an inch thick, and the 

 extremes of the long axis about a 4- of an inch, or half the other. The sclerotic 

 coat becomes thinner as it approaches to its union with the cornea, where it is 

 thin and ^oft. It is extremely firm in its texture where thick, and from a trans- 

 verse section would seem to be composed of tendinous fibres, intermixed with 

 something like cartilage; in this section 4 passages for vessels remain open. This 

 firmness of texture precludes all effect of the straight muscles on the globe of 

 the eye, by altering its shape, and adapting its focus to different distances of 

 objects, as has been supposed to be the case in the human eye. The cornea 

 makes rather a longer ellipsis than the ball of the eye; the sides of which are not 

 equally curved, the upper being most considerably so. It is a segment of a 

 circle somewhat smaller than that of the eyeball, is soft and very flaccid. The 

 tunica choroides resembles that of the quadruped; and its inner surface is of a 

 silver hue, without any nigrum pigmentum. The nigrum pigmentum only 

 covers the ciliary processes, and lines the inside of the iris. The retina appears 

 to be nearly similar to that of the quadruped. The arteries going to the 

 coats of the eye form a plexus passing round the optic nerve, resembling in its 

 appearance that of the spermatic artery in the bull and^ome other animals. 



