ANATOMY. 



tre. The lens is contained in its proper 

 capsule, the posterior surface of which 

 adheres firmly to the tunica hyaloidea; 

 but its separation can sometimes be effect- 

 ed without rupturing it. It has no appa- 

 rent connection to this capsule. It is an 

 opaque state of this body that constitutes 

 the disease called cataract. 



The aqueous humour is a small quantity 

 of transparent water, placed immediately 

 behind the cornea, and occupying the 

 space between that membrane and the 

 crystalline lens : it is easily reproduced 

 when let out. 



In the midst of the space occupied by 

 this humour the iris is found, and it di- 

 vides the space into two portions, called 

 the anterior and posterior chambers of the 

 eye ; which communicate by means of the 

 pupil. The anterior is much the largest 

 of these. 



The choroid coat, ciliary processes, and 

 iris, are very vascular, and derive their 

 supply from the ciliary branches of the 

 ophthalmic artery. 



The iris is very largely supplied with 

 nerves from a small ganglion, named len- 

 ticular, formed on a branch of the nervus 

 motor, or nerve of the third pair. These 

 are called the ciliary nerves. 



Of tfie eye-lids andlacrymal apparatus. 

 The eye-ball is covered by two moveable 

 curtains, formed by a folding of the com- 

 mon integument, and called the eye-lids. 

 In order to keep these uniformly expand- 

 ed, and to prevent them from forming 

 wrinkles, each of them contains a thin 

 portion of cartilage, adapted in figure to 

 the convexity of the globe, and called the 

 tarsus. In order to provide still further 

 for the greatest possible facility of motion, 

 the eye-lids fare lined by a smooth and 

 polished membrane, and the globe of 

 the eye is covered by the same membrane, 

 on its anterior part : this is called con- 

 junctiva, as it serves to connect the front 

 of the eye-ball to the eye-lids. 



The junctions of the eye-lids are called 

 the internal and external canthus, or angle 

 of the eye. 



They are opened by the levator palpe- 

 brae lifting up the upper lid ; and this mus- 

 cle is in a state of constant action so long 

 as we keep our eyes open. They are 

 closed by the circular orbicularis palpe- 

 brarum. 



The cilia, or eye-lashes, are two rows 

 ot strong curved hairs implanted in the 

 opposed edges of the two eye-lids, and 

 admirably calculated for protecting the 

 eye from dust or other foreign bodies. 



The hairy prominences above the eye- 

 iids are Uie supercilia, or eye-brows; these 



are very moveable ; they serve as a pro- 

 tection to the eyes, and are much con- 

 cerned in expressing the passions. 



In order to facilitate the motions of the 

 eye-lids and eye-balls on each other, the 

 surface of the conjunctiva is constantly 

 moistened by a watery and mucilaginous 

 fluid, poured out by the arteries of the part. 

 The incrustations of the mucilage in the 

 night would glue the eye-lids together ; 

 but this effect is obviated by a natural oint- 

 ment, formed in a very elegant grandular 

 apparatus on the inner surface of the tarsi. 

 We there find about 16 or 17 longitudinal 

 parallel rows of very minute glandular bo- 

 dies ; and these pour out their sebaceous 

 secretion from a series of apertures on the 

 edges of the eye-lids. They are called 

 the meibomian glands, and ciliary ducts. 



The fluid just described is constantly 

 formed on the surface of the conjunctiva ; 

 but on extraordinary occasions, as when an 

 irritating foreign body is in the eye, or in 

 consequence of affections of the mind, a 

 fluid is poured out in greater abundance, 

 which has the name of tears, and is secret- 

 ed by the lacrymal gland. This is a small 

 conglomerate gland, situated in the orbit, 

 near the upper eye-lid, and having ducts 

 which terminate on the surface of the con- 

 junctiva ; but which, on account of their 

 minuteness, are hardly demonstrable in the 

 human subject. The utility of this secre- 

 tion in washing away any foreign substance 

 must be sufficiently obvious. 



The superfluous part of the lacrymal se- 

 cretion is conveyed through two very fine 

 tubes to a small bag, situated at the inter- 

 nal angle of the eye. These tubes com- 

 mence by open mouths, called the puncta 

 lacrymalia, from the inner extremities of 

 the eye-lids, and are about equal in size 

 to admit a hog's bristle. 



There is a little fleshy projection at the 

 corner of the eye, and between the two 

 puncta, called caruncula lacrymalis. 



The lacrymal sac is a small membranous 

 bag, placed in the hollow formed at the 

 inner edge of the orbit. The tendon of 

 the orbicularis palpebrarum, which gene- 

 rally forms a slight eminence visible 

 through the skin, crosses the middle of 

 this bag. 



A canal, called the ductus nasalis, and 

 lodged in a groove of the superior maxil- 

 lary bone, conveys the tears into the nose; 

 where it terminates by an open orifice 

 within the inferior turbinated bone. 



ORGAN OF HEARING. 



The organ is divided into two parts, the 

 external and internal ear, by the membra- 



