388 



ANATOMY IN A NUTSHELL. 



the frontal bone resting on the eye-ball and the Superior rectus and External 

 rectus muscles. It is about the shape and size of an almond. It is constricted 

 in ihf center. The ducts, about seven, pass through the conjunctiva, opening 

 on the outer part of the upper lid. The lachrymal canals, two in number, begin 

 at the puncta lachrymalia in each lid, the superior one passing upward and then 

 inward to join the inferior one which passes downward and then inward. They 

 empty into the lachrymal sac together. The lachrymal sac lies in a groove 

 formed by the lachrymal bone and nasal process of the superior maxillary. It 

 is the dilated upper part of the nasal duct. It is crossed by the Tensor tarsi and 

 is covered by an expansion from the tendo oculi. The duct is about one-half 

 an inch long and directed downward, slightly outward and backward. It is 

 formed by the lachrymal, superior maxillary, and inferior turbinated bones. It 

 extends from the lachrymal to the inferior meatus of the nose where it opens. 

 The opening has a valve formed by the mucous membrane. 



PLATE CCIV. 



MOALJJNE 

 OPTICAL. AXJS 



FOVEA CENTRALIS 

 OR CENTRAL PIT 



OF THE 

 MACULA LUTEA. 



Optical Axis and Visual Line. 



LESSON CVIX. 



The conjunctiva (joined together) which unites the eyelids and the eye-ball 

 is a mucous membrane. It lines each eyelid at the base of which it is reflected 

 mi the eye-ball. The lines of reflection are the fornices. The supeiior one is 

 the deeper and some of the fibers of the Levator palpebral are inserted into it. 

 The conjunctiva is loosely attached to the sclerotic cord, but at the outer mar- 

 gin of the cornea it is firmly attached, passing over the cornea, forming its in- 

 ferior epithelial layer. The ducts of the lachrymal gland open into the con- 

 junctival sac above and the opening of the lachrymal canaliculi at the puncta 

 lachyrymalia below. The palpebral conjunctiva is sensitive, vascular and 

 thick. Pari of the eye-ball or ocular conjunctiva is thin, transparent and is only 

 slightly vascular in the healthy condition. The plica semilunaris is a fold of 

 conjunctiva at the inner canthus of the eye. It is the rudimentary homologue 

 of the membrana Nictitans (third eyelid) in birds. (Plates CCV-CCIX). 



