ACCESSORY ORGANS OF VISION. 



233 



and inner part of the floor of the orbit, near the lachrymal groove ; 

 pass under the eyeball, and are inserted between the entrance of the 

 optic nerve and insertion of the abductor oculi, and opposite the inser- 

 tion of the obliquus superior. These muscles have their proper nerves. 

 The third pair motores oculorum or common oculo-muscular, are dis- 

 tributed to all the muscles except the trochlearis and abductor; the 

 fourth pair or pathetic or internal oculo-muscular, to the trochlearis 

 singly ; and the sixth pair or external oculo-muscular, to the abductor. 



Fig. ill. 



Fig. 112. 



Posterior View of the Eyelids and Lachrymal Gland. 



1,1. Orbicularis palpebrarum muscle. 2. Borders of 

 the lids. 3. Lachrymal gland. 4. Its ducts opening in 

 the upper lid. 5. Conjunctiva covering the lids. 6. 

 Puncta lachrymalia. 7. Lachrymal caruncle as seen 

 from behind. 



Lachrymal Canals. 



1. Puncta lachrymalia. 2. Cul-de-sac 

 at the orbital end of the canal. 3. Course 

 of each canal to the saccus lachrymalis. 

 4,5. Saccus lachrymalis. 6. Lower part 

 of the ductus ad nasum. 



The office of tutamina oculi is not wholly engrossed by the parts 

 that have been mentioned. The apparatus for the secretion of the 

 tears participates in it, by furnishing a fluid, which lubricates the sur- 

 face of the eye, and keeps it in the necessary degree of humidity for the 

 proper performance of its functions. It is a beautiful, and ingenious 

 little apparatus ; the structure of which can easily be made intelligible. 

 It consists of the lachrymal gland; the excretory ducts of the gland; the 

 caruncula lachrymalis; the lachrymal ducts; and the nasal duct; in 

 other words, of two sets of parts, one, forming the fluid and pouring 

 it on the anterior surface of the eye; the other comprising the organs 

 for its excretion. The lachrymal gland is situate in a small fossa or 

 depression at the upper, anterior, and outer part of the orbit. It is an 

 oval body of the size of a small almond; of a grayish colour; and com- 

 posed of small, whitish, granular bodies collected into lobes. From 

 these, six or seven excretory ducts arise, which run nearly parallel to 

 each other, and open on the inner side of the upper eyelid, near the 

 outer angle of the eye and the tarsal cartilage. Through these ducts, 

 the tears, secreted by the lachrymal gland, are spread over the tunica 

 conjunctiva. They are not secreted by animals that live in water. 



At the inner angle of the eye is the caruncula lachrymalis. It is a 



