212 



VISCERAL ANATOMY. 



FlG I0 5- evaporates, or collects in lacus and 



passes through puncta into canaliculi, 

 and so to lachrymal sac, and thence, 

 by the nasal duct, into the inferior 

 meatus of the nose. 



What are the Canaliculi ? They are 

 two minute canals, -fa inch in diameter 

 and y z inch long, which extend from the 

 punctum in each lid to the lachrymal sac. 

 They are lined with mucous membrane, and 

 enveloped by fibres of the tensor tarsi muscle. 



Describe the Lachrymal Sac. It is 

 the superior dilated extremity of the nasal 

 duct, and is situated in the groove formed by the lachrymal bone and the 

 nasal process of the superior maxillary. Its form is oval, flattened antero- 

 posteriorly ; its dimensions about f inch long and \ inch wide. Its fundus is 

 crossed by the tarsal ligament, and by the tensor tarsi muscle. Its junction 

 with the nasal duct may be interrupted by folds of the lining mucous mem- 

 brane. 



What is the Nasal Duct ? A membranous canal extending from the 

 lachrymal sac to the inferior meatus of the nose. It is about ^ inch long, ^ 

 inch in diameter, is contained in the osseous lachrymal canal, curving down- 

 wards, backwards and outwards, and its calibre is narrowest about its middle. 

 Its mucous lining is thick, and continuous with the Schneiderian membrane of 

 the nasal cavity. Surrounding it is a vascular network of connective tissue, 

 and outside this, a tendinous sheath. At its lower end a fold of mucous mem- 

 brane forms an imperfect valva. 



THE EAR. 



What Bone contains the Auditory Apparatus ? The petrous and mas- 

 toid portions of the Temporal bene. [Described on page 16.] 



Name the Divisions of the Auditory Apparatus. The organ of hear- 

 ing consists of the following parts, viz. 



f Auricle, or Pinna. 



\ External Auditory CanaL 



f Membrana Tympani. 



Cavity of the Tympanum. 



2. Middle Ear, or Tympanum { ' J 



| Mastoid Cells. 



) JLustachian Tube. 



