THE HEAD 



11 



behind, the parotic? gland; and below, the cheek. This region is impor- 

 tant, not only because it embraces within its area the joint by which the 

 lower jaw is hinged on to the head, but also on account of the temporal 

 artery which crosses it near to the surface. 



Supra-orbit (fig. 2). — The supra-orbit is a somewhat rounded space 

 situated above the eye and between the forehead in front and the temple 

 behind. It contains a mass of soft loose fat, which in the young animal is 

 very abundant, and quite, or nearly, fills up the cavity. As age advances, 

 the fatty matter becomes less and less considerable, until in old animals a 

 deep hollow appears, known as the " hollow of the eye ". 



To a certain extent this change in the fulness of the cavity serves to 

 distinguish an old from a young animal, but it cannot be said to be 

 at all times reliable. In very poor colts the fat becomes in a large 

 measure absorbed, in which case an 

 expression of advanced age is im- 

 parted to the face. This, however, 

 disappears again as soon as the horse 

 recovers his condition. 



Orbital - arch or Eyebrow 



(fig. 2). — The orliital-arch is the pro- 

 minent crescent-shaped ridge which 

 spans the upper surface of the globe of 

 the eye. It forms the anterior limit 

 of the hollow of the eye, and is the 

 base of attachment of the upper eyelid. 

 The Eye. — The eye occupies a 

 deep bony cavity on the side of the 

 forehead and beneath the orbital- 

 arch. It is protected by two movable 

 curtains, the upper and lower eyelids 

 and their appended lashes, which not 

 only serve to protect from and to dis- 

 place any foreign matter that may fall 



upon it, but also assist in regulating the amount of light passing into it. 

 The parts visible in ordinary observation of this organ are — 1, a dense 

 opaque membrane, the sclerotic or "white of the eye"; 2, a central trans- 

 parent membrane, the cornea. These form the outer capsule in front, 

 within which may be noticed 3, a yellowish-brown ovoid membrane, the 

 iris, encircling a clear dark space, 4, the pupil. An examination of the 

 inner corner of the eye reveals a flat fleshy-looking body termed the mem- 

 brana nictitans, or, commonly, the third eyelid or "haw" (fig. 8). This 



Fig. 8. — Examination of («) the Haw 

 or membrana uictitans 



