Chap. VI. The Anatomy of a HORSE. 45 



and is call'd the Retina^ becaufe it encompalleth the glafly 

 Humour like a Net. By a Combination of the Rays of 

 Light on the fine Filament of this Coat, and the Refiedion 

 which is caufed by the Opaquenefs of the Sclerotica, and the 

 Blacknefs of the Infide of the Uvea, all external Images are 

 conveyed diftind to the Imagination ; whereas if the Rays 

 were not thus colleded on the Retina , there would be no 

 fuch Thing as diftin6l Vifion. 



The Humours of the Eye, which come next to be con- 

 fider'd, are in Number three. 



The cutermoft is called the aqueous, or ^ke aqueous 

 watery Humour, being thin and fluid, like Humour, 

 Water j it fills up the Space between the Cornea and Cry- 

 ftalline Humour in the forepart of the Eye. 



The Cryfialline is the next, fo called fT/^^ Chriftal- 

 from its Brightnefs, being clear and tranfpa- hne Humour. 

 rent, like Cryital ; it is inclofed in the vitreous or glafly 

 Humour ; it is look'd upon to be the chief Inftrument 

 whereby the Fays of Light are collected upon the filamen- 

 tous Expanfiun of the Retina, 



The iaft is called the glajfy Humour : It 57'^ vitreous 

 is not fo folid as the Cryftalline, but exceeds Humour. 

 both it and the watery Humour in Quantity ;' it is partly 

 convex, excepting that Cavity where it receives and fur- 

 rounds the Cryftalline. It is not fo bright as the Cryftal- 

 line, but yet tranfparent, that the vifible Species, received 

 into the Cryftalline Humour, might not be reflected on be- 

 fore they reach the Retina^ but Ihould be tranfmitted to it 

 pure and unmix'd. 



§ V. Of the Ears. 



The Ear is divided into the External and ^^^ ^^^ 

 Internal ; the External is that Part which a 

 Horfe moves backward and forward at Pleafure, and is fo 

 well known, that there needs but little to be faid about it. 

 Its Ufe is partly for Ornament, and partly to gather all 

 Sounds, and tranfmitthem to the Internal. 



The Internal Ear confifts of feveral Parts, I^^ Parts, 

 which are very curious, and are feated m the 

 Cavity of the Os petrofum. 



The firft of thefe is the Drurn, with its tj-jy^j)..^ 

 Cord and Mufcles. The Drum is a very thin 

 and tranfparent Membrane, being an Expanfion of the foft- 

 er Procefsof the Auditoiy Nerve i it is very dry, that it 



may 



