498 THE ANATO:\IY OF THE HORSE 



outwards so as to partially cover it when the muscles retract the eye, and 

 for want of space drive it forward. This happens whenever the eye is 

 irritated either by an insect or by the dust or hayseeds which are so often 

 deposited upon the conjunctiva, and which, causing the eye to be drawn 

 back, displace the fat deposited on the back of the orbit, and this again 

 pushes forward the haw. For this reason in all irritable states of the eye 

 the haw is prominent. 



The barbarous practice of excising it as an offending body has happily 

 ceased with the advent of skilled veterinary surgeons. The muscles move the 

 eye in all dii-ections, and have the peculiar property of keeping the long 

 diameter of the pupil always nearly in a line parallel with the horizon. 

 Practically they are not of any great importance. The lachrymal apparatus 

 consists of the lachrymal gland, situated beneath the outer wall of the orbit, 

 and secreting the tears, which are intended to wash the conjunctiva clear of 

 any foreign body. The secretion is thrown out upon its surface through a 

 number of small ducts, and traversing from the outer angle to the inner, is 

 conducted through two small openings in the lids to the lachrymal sac, and 

 from that by the nasal duct to the nose. 



THE EAR 



Tins organ is divided into the external ear for collecting the waves of 

 sound, and conveying them inwards, and the internal ear which is situated 

 within the petrous part of the temporal bone. The latter is a very com- 

 plicated and delicate organ ; but its formation does not differ in any essential 

 features from that of the other vertebrate animals, nor are the diseases 

 attacking it in the horse of any particular importance, so that its description 

 will be omitted. 



THE ORGAN OF TOUCH 



The sense op touch is necessary for the proper appreciation of the 

 mechanical form and nature of the objects placed in apposition to the body, 

 and of their temperature. It is seated generally in the tei'minations of 

 the nerves of sensation on the skin ; but there are certain parts specially 

 endowed with these nerves, which in the horse are the lips and the four 

 extremities. 



The skin is composed of two layers, one internal and living termed the 

 dermis or chorion, the other a secretion from it, and called the epidermis, 

 the inner and freshly secreted layer of which is the rete mucostim of the 

 old authors. The dermis constitutes nearly the whole substance of the skin, 

 and varies in thickness in different regions of the body, and also in the 

 nature of its attachment to the subjacent parts, being very loosely connected 

 in some, and in others so tight that it cannot be pinched up. It consists of 

 a layer of cellular and elastic fibres crossing each other in all directions, and 

 abundantly supplied with blood-vessels and nerves. Its external surface is 

 provided with numberless little elevations termed papillia^, each of which 

 contains the termination of a nerve : and it is pierced with an immense 



