THE DISEASES OF CATTLE. 231 



The seventli and last muscle to be described, is the retractor; 

 it is one of the most admirably arranged muscles in the whole 

 animal economy ; in figure it resembles a hollow cone ; its 

 apex turned backwards ; its base pointing forwards, the inner 

 edge surrounding the optic foramen, and at the same time 

 offering protection to the optic nerve. Around its sides, equi- 

 distant, are found the four recti muscles, making a very com- 

 plex and wonderful piece of mechanism. The action of this 

 muscle is to draw the eye backw^ards within the orbit. 



I shall now make some brief yet instructive allusions in 

 relation to the appendages of the eye. The appendages com- 

 prise the eyelids, eyelashes, tarsal cartilages, meibomian glands, 

 membrana nictitans, lachrymal glands, caruncula lachrymalis, 

 puncta lachrymalia, lachrymal sac, and ductus ad nasum. 



Eyelids. — The upper and lower eyelids may be considered 

 as the .movable blinds of the eye ; the upper is the most 

 capable of corrugation, and borders the greatest surface of the 

 eyeball ; it is readily resolved into wrinkles. At the junctures 

 of the aperture which separates the eyelids, are the canthi or 

 angles of the eye. The loose portion of integument entering 

 into the composition of the upper lid, is derived from the skin 

 covering the frontal region ; and that of the lower lid is derived 

 from the face. -The lids, internally, form two cavities, thus 

 adapting themselves to the convexity of the globe ; their in- 

 ternal surfaces are lined with the tunica conjunctiva. The 

 borders of the eyelids have two margins ; on the outer one 

 we find eyelashes; betw'een the latter and the internal margin, 

 we find the orifices of the ciliary glands through which issue 

 a secretion, for the lubrication of the surrounding parts. The 

 edge, or surface between the two margins just alluded to, con- 

 duct the tears into the puncta lachrymalis. 



Eyelashes. — The eyelashes {cilia), are so familiar to the 

 reader, and their function is so apparent, that I need not trouble 

 them with any remarks about them, only to observe, that by 

 their advantageous arrangement, the rays of light, come from 

 whatever direction they may, are somewhat intercepted, and 

 they also operate as feelers to the seeing as well as the sight- 



