OKGANS OF THE SENSES. 



IN this Part will be described the organs of sight, hearing, and smell, and also 

 the taste buds which are found on the tongue and other parts endowed with the 

 sense of taste. The terminations of sensory nerves in the skin and elsewhere have 

 already been described in Vol. I., Part 2, and will only be briefly alluded to in 

 reviewing the whole subject of the ending of nerves of special sense. 



THE EYE. 



The organ of vision, strictly speaking, consists only of the ball or globe of the 

 eye ; but connected with the eyeball externally are muscles, nerves, and blood- 

 vessels, elsewhere described, as well as other parts specially destined for its protec- 

 tion (tutamina oculi), of which an account will first be given. 



THE EYELIDS AND CONJUNCTIVA. 



The eyelids (palpebrce) are moveable folds of integument, strengthened towards 

 their margins by a thin lamina of dense fibrous tissue (tarsus). They are about 

 3mm. thick near their free edge. A mucous membrane (conjunctiva) lines their 

 inner surface, and is reflected thence on the front of the eyeball. The line of 

 reflection is termed thefornix conjunctives. 



Fig. 1. FRONT VIEW OF THE RIGHT EYE, WITH THE 



EYELIDS DRAWN APART BY BLUNT HOOKS. (Merkel.) 



Ps, plica semilunaris ; Pis, Pli, punctum lacrimale 

 sup. et inf. ; Car, caruncula lacrimalis ; Lpm, interna 

 tarsal ligament. 



The upper lid is larger and more moveable 

 than the lower, all the transparent part of the 

 globe being covered by it when the eye- is 

 closed ; it is chiefly by the elevation of this lid 

 that the eye is opened, the movement being 

 effected by a muscle (levator palpelra) devoted 

 exclusively to this purpose. At the outer and 

 inner angles (canthi) of the eye the eyelids are 

 united. The interval between the angles varies 



in different individuals, averaging about 28mm. (Fuchs), and, according to its 

 extent, gives the appearance of a larger or a smaller eye, the size of the globe being 

 nearly the same in all. The greater part of the edge of each eyelid is flattened 

 and angular, but towards the inner canthus it is rounded off for a short space, at 

 the same time that it changes its direction, so that a rounded bay is here left 

 between the two eyelids ; this bay has been termed the lachrymal reservoir (lacus 

 lacrimalis) ; at this point there is seen on each lid a slight elevation (papilla 

 lacrimalis), the apex of which is pierced by the aperture (punctum) of a small 

 canal (canaliculus lacrimalis) which serves to convey away the fluid which moistens 

 the conjunctiva (fig. 1, Pli, Pis). (See also figs. 9, 10, and 11.) 



In the greater part of their extent the lids are applied to the surface of the eye- 

 ball ; but at the inner canthus, at the lachrymal lake, there intervenes a vertical fold 



VOL. III. PT. 3. B 



