THE EAR. 233 



cboroid, and their inner portions, adjoining and between the 

 rods and cones, studded with pigment-granules. 



In the macula lutea the rods are absent and some of the 

 retinal layers are thickened and pigmented yellow. At the 

 fovea centralis only the layer of cone-cells is present in full 

 development, the layers in front of it i. e., toward the centre 

 of the globe being greatly thinned and nearly abolished. 



The eyelids (upper) are covered anteriorly with thin skin, 

 beneath which is areolar subcutaneous tissue containing little 

 or no fatty tissue. Next to this is a layer of striated muscle, 

 the orbicularis palpebrarum. Posterior to this is a zone of 

 loose connective tissue, the fascia palpebr alls, into which the 

 insertion of the levator palpebra? merges. Posterior to this 

 and next to the conjunctiva is a dense fibrous plate, the 

 tarsus, in which are imbedded a number of modified seba- 

 ceous glands, the Meibomian glands, each consisting of an 

 elongated series of follicles opening into a duct which dis- 

 charges at the margin of the lid. 



In the upper part of the tarsal plate, especially toward the 

 nose, are small accessory lachrymal glands. The posterior 

 surface of the lid is covered by conjunctiva, composed of 

 stratified columnar epithelium on a tunica propria, which lies 

 next to the tarsus. 



At the margin of the lid is a row of stiff hairs, the eye- 

 lashes, the follicles of which separate the margin of the 

 orbicularis palpebrarum from the main portion of the muscle ; 

 behind the lashes are modified sweat-glands (Moll's glands) ; 

 and still farther posteriorly are the openings of the Meibomian 

 glands. 



The lachrymal gland is a racemose gland of the serous type, 

 the saccules of which empty into a number of independent 

 and separate outlet-ducts. The lachrymal canals are tubes 

 lined with mucous membrane connecting the conjunctive with 

 the nasal fossa?. 



The Ear. 



The ear is a complicated structure associated with the term- 

 ination of the nerves of hearing, and \vith the sense of 

 position. It is divided into the external, middle, and internal 

 ear. 



