416 THE HORSE. 
muscles move the eye in all directions, and have the peculiar property of 
keeping the long diameter of the pupil always nearly in a line paralle! 
with the horizon. Practically they are not of any great importance 
The lacrumal apparatus consists of the lacrymal gland, situated beneath 
tne 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 lacrymal sac, and from that by the nasal duct 
to the nose. 
THE EAR. 
THIS 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 OF 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 termina- 
tions 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 
epudermis, the inner, and freshly secreted layer of which is the rete 
mucosum 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 eleva- 
tions termed papille, each of which contains the termination of a nerve: 
and it is pierced with an immense number of holes; some of which allow 
the hairs to pass through, others are the pores through which the sweat is 
poured out, and others again are follicles for the secretion of sebaceous or 
half-oily fluid, for the purpose of lubricating the skin. These last are 
particularly numerous at the flexures of the joints, as at the inner part of 
the hock, knee, and heel, in each of which situations they are liable to 
become clogged, leading to the conditions known as mallenders, sallenders, 
and cracked heels, which will be hereafter described. 
THE EPIDERMIS, cuticle, or scarf-skin, is very thin but tough, and in the 
horse its innermost layer is generally of a dark slate colour, the better to 
protect the dermis from the rays of the sun. It is composed of scales 
agglutinated together, and its internal surface is reflected in the form of 
fine sheaths around all the hairs which pierce it, and of linings to the 
sweat pores and sebaceous follicles. As fresh cuticle is secreted the outer 
layers fall off; and in the horse this growth is very rapid, so that in a very 
