T!IR SI^XSORIAL PUXCTIO:^. L5s> 



transparent part of it insects or dust tliat may annoy the animal. What 

 becomes of these impurities when thus washed off ? Ai-e they carried by 

 the tears to the corner of the eye, and so pass down this duct, and irritate 

 and obstmct it ; or do they accumulate at the inner angle of the eye ? 

 There is a beautiful contrivance for disposing of them as fast as they accu- 

 mulate. Concealed within the inner corner of the eye, or just at the 

 margin of it, black or pied, is visible a triangular-shaped cartilage, the haiv., 

 with its broad part forwards. It is concave witliin, exactly to suit the 

 globe of the eye ; it is convex without, accurately to adapt itself to the 

 membrane Hning the lid ; and the base of it is reduced to a thin or almost 

 sharp edge. At the will of the animal this is suddenly protruded n-om 

 its liiding-place. It passes rapidly over the eye, and shovels up every 

 nrdsance mixed with the tears, and then being speedily drawn back, the 

 dust or insect is wiped away as the cartilage again passes under the comer 

 of the eye. 



How is this managed ? The cartilage has no muscle attached to it ; 

 and the limbs and the different parts of the body, when put into motion 

 by the influence of the will, are moved invariably by muscles. The 

 mechanism, however, is simple and effectual. There is a considerable 

 mass of fatty matter at the back of the eye, in order that this organ may 

 be easily moved ; and this fat is particularly accumulated about the inner 

 corner of the eye, and beneath, and at the point of this cai-tilage. The 

 eye of the horse has likewise very sti'ong muscles attached to it, and one, 

 peculiar to quadrupeds, of extraordinary power, by whose aid, if the animal 

 has not hands to ward off a danger that tlxreatens, he is at least enabled to 

 di-aw the eye back almost out of the reach of that danger. 



Dust, or gravel, or insects, may have entered the eye, and annoy the 

 horse. This muscle suddenly acts : the eye is forcibly di'awn back, and 

 presses upon the fatty matter. That may be displaced, but cannot be 

 reduced into less compass. It is forced violently towards the inner corner 

 of the eye, and it drives before it the haw ; and the haw, having likewise 

 some fat about its point, and being placed between the eye and an exceed- 

 ingly smooth and polished bone, and being pressed upon by the eye as it 

 is violently drawn back, shoots out with the rapidity of lightning, and, 

 guided by the eyelids, projects over the eye, and thus carries off the 

 offending matter. 



In what way shall we di'aw the haw back again without muscular 

 action ? Another principle is called into play, of which mention has 

 already been made, and of which we shall have much to say — elasticity. 

 It is that principle by which a body }delds to a certain force impressed 

 upon it, and returns to its former state as soon as that force is removed. 

 It is that by which the ligament of the neck (p. 153), while it supports 

 the head, enables the horse to graze — by which the heart expands after 

 closing on and propelling forward the blood in its ventricles and the 

 ai'tery contracts on the blood that has distended it, and many of the most 

 important functions of life are influenced or governed. This muscle ceases 

 to act, and the eye resumes its natural situation in the orbit. There is 

 room for the fatty matter to return to its place, and it immediately returns 

 by the elasticity of the membrane by which it is covered, and draws after 

 it this cartilage with which it is connected, and whose return is as rapid as 

 was the projection. 



The old farriers strangely misunderstood the nature and desigii of the 

 liaw, and many at the present day do not seem to be much better informed. 

 \'Vlien, from sympathy with other parts of the eye labouring under in- 

 /laramation, and becoming itself inflamed and increased in bulk, and the 

 neighljouiing parts like^^^se thickened, it is either forced out of its j^J^ce, 



