126 THE SENSORIAL FUNCTION. 



conveyed by a long canal, the lacrymal duct, partly bony, and partly membran- 

 ous, to the lower part of the nose. A little within the nostril, and on the divi- 

 sion between the nostrils, is seen the lower opening of this canal ; the situation 

 of which should be carefully observed, and its real use borne in mind, for not 

 only horsemen, but even some careless veterinary surgeons, have mistaken it 

 for a glanderous ulcer, and have condemned a useful and valuable animal. It 

 is found just before the skin of the muzzle terminates, and the more delicate 

 membrane of the nostril commences. The opening of the canal is placed thus 

 low because the membrane of the nose is exceedingly delicate, and would be 

 irritated and made sore by the frequent or constant running down of the tears. 



There is, however, something yet wanting. We have a provision for sup- 

 plying the eye with requisite moisture, and for washing from off the transparent 

 part of it insects or dust that may annoy the animal. What becomes of these 

 impurities when thus washed off? Are they carried by the tears to the corner 

 of the eye, and so pass down this duct, and irritate and obstruct 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 accumulate. Concealed within the inner 

 corner of the eye, or only the margin of it, black or pied, visible, is a triangu- 

 lar-shaped cartilage, the haw, with its broad part forwards. It is concave 

 within, exactly to suit the globe of the eye ; it is convex without, accurately to 

 adapt itself to the membrane lining 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 

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

 nuisance mixed with the tears, and then, being speedily drawn back, the dust 

 or insect is wiped away as the cartilage again passes under the corner 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 particu- 

 larly accumulated about the inner corner of the eye, and beneath, and at the 

 point of this cartilage. The eye of the horse has likewise very strong 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 threatens, he 

 is at least enabled to draw 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 drawn 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 exceedingly 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 draw 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 yields 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. 112), 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 artery contracts on the blood that has distended it, and many 

 of the most important functions of life are influenced or governed. This muscle 



