142 



ANATOMY AND PHYSIOLOGY OF 



being coated it detains any small foreign bodies that 

 may float in the lachr}Tnal secretion ; it also directs 

 the latter fluid into the puncta. 



LACHRYMAL PLTsXTA AXD CONDUITS. 



Q. "\Miat are the pimcta lachrj-malia ? — A. Two small 

 orifices situated on the inward margins of the two lids — 

 superior and inferior — near the radix of the caruncle. 



Q. What do the puncta terminate in? — A. The 

 lachrj-mal conduits. 



Q. AMiat is their situation? — A. Withm the sub- 

 stance of the eyeHds. 



Q. How are conduits formed ? — A. A minute carti- 

 laginous circle surrounds them, and they are Hned by 

 conjunctival membrane. 



Q. What do the conduits terminate in? — A. The 

 lachrjmal sac. 



LACHRYMAL SAC. 



Q. Where is the lacluymal sac situated ? — A. With- 

 in the depression which leads into the channel of the 

 lachr^-mal bone, beliind and below the small eminence 

 upon the orbital ridge of that bone. 



Q. Describe tlie sac and its connections ? — A. It is 

 an oblong membranous bag; its front is crossed by 

 fibres of the orbicularis ; it has also a connection with 

 the tendon of that muscle. The j^osterior part of the 

 sac adheres fii-mly to the lachrymal bone. It is com- 

 posed of a dense, white, fibrous membrane, fiimished 

 with a lining from the conjunctivia. 



Q. By what is this sac perforated ? — A. By the 

 lachrjmal conduits. 



Q. What does it open into ? — A. Into the ductus ad 

 nasiun. 



Q. What is the function of this sac? — A. It is a 

 reservoir into which the tears flow from the lachrymal 

 conduits, and fi'om thence pass into the ductus ad 

 nasum. 



DUCTUS AD NASUM. 



Q. "WHiat is the ductus ad nasum? — A. It is a long 

 membranous canal, commencmg at the contracted por- 

 tion of the lachi-ymal sac, and rumiing with the groove 

 through the lachrj-mal bone ; then along a canal in the 

 superior maxillary bone, between it and the anterior 

 turbinated bone ; terminating at the imier and inferior 

 part of the nostril. 



Q. What is the organization of the ductus ? — A. It 

 appears to be a continuation of the membrane com- 

 posing the lachrymal sac, Avhich is strengthened by a 

 fibrous sheath ; its internal surface is probably mucous, 

 which protects it from the action of the tears, or 

 lachrjTnal secretion. 



Q. Describe the course of the tears, or lachrj-mal 

 secretion ? — A. They are secreted by the lachi-ymal 

 gland, and ai-e pom-ed by its excretory ducts over the 

 sm'face of the eyeball ; the puncta lachrj-malia absorb 

 them ; they are then conveyed by the lachrjuial ducts 

 to the lachrjTnal sac ; and through the ductus ad nasiun 

 pass into the nostril. 



THE EYEBALL AND ITS COATS. 



Q. What is the form of the globe of the eye? — A. 

 Nearly of a spherical figure. 



Q. Of what is the globe of the eye composed? — A. 

 Of membranes, or coats, filled with humoi's or fluids, 

 which preserve its form. 



Q. How many coats has the ej-e ? — A. Five : the 

 sclerotic, choroid, retina, cornea, and iris. 



Q. Does not the tunica conjuncti\ia enter into the 

 com j^osition of the membranes of the eye? — A. Yes: 

 it may be considered as common to both. 



Q. Where does it adhere most closely? — A. Over 

 the cornea. 



SCLEROTIC COAT. 



Q. What is the use of the sclerotica ? — A. It bomids 

 the form of the eye, protects and supports the parts 

 within. 



Q. What are its perceivable boundaries ? — A. It ex- 

 tends from the optic nerve to the cornea. 



Q. What is inserted into it posteriorly? — A. The 

 fleshy part of the retractor muscle. 



Q. What is inserted into its anterior margins ? — A. 

 The tendons of the four* recti. 



CORNEA. 



Q. What is the comea ? — A. The transparent, ante- 

 rior part of the globe of the eye. 



Q. How does its form compare with the sclerotica ? — 

 P. It is more convex. 



Q. What covers its convex surface ? — A. The con- 

 jmicti^da. 



Q. What is its structure? — A. Laminated. 



IRIS. 



Q. What is the iris ? — A . It is a circular membrane, 

 with an irregular central ca^•ity, in the anterior chamber 

 of the eye. 



Q. What is its central perforation called ? — A. The 

 pupil. 



Q. How is the periphery of the pupil bounded ? — A. 

 By several dark, colored, glandular bodies, termed cor- 

 pora nigra. 



Q. What is the use of the iris? — A. By contracting 

 it excludes all superfluous rays of light, and by expand- 

 mg admits tlirough the pupil all that pass through the 

 cornea. 



Q. What is the structure of the iris? — A. It is a 

 fibrous membrane, divisable into two layers, provided 

 with blood-vessels and nerves. 



CHOROID COAT. 



Q. What is the choroid coat ? — yl. It is a dark- 

 colored membrane of dehcate textm-c, located immedi- 

 ately beneath the sclerotica. 



Q. What are its boundaries? — A. It extends from 

 around the termination of the optic nerve as far for- 

 ward as the edge of the cornea, and ends in the ciliary 

 circle. 



