HISTOLOGY. 



The cells of the other form are low when full of secretion, which gathers in 

 a large round mass, leaving only a thin basal layer of protoplasm. Inter- 

 cellular secretory capillaries and secretory granules have been demon- 

 strated. Between the gland cells and the basement membrane there are 

 occasional flat cells, a continuation of the deeper layer of the epithelium 



of the duct. The blood ves- 

 sels and nerves are similar 

 to those of the oral glands. 

 The two lachrymal 

 ducts which at the medial 

 angle of the eye connect 

 with the nasolachrymal duct. 

 must not be mistaken for 

 the excretory ducts of the 

 lachrymal glands. The for- 

 mer consist of stratified 

 epithelium with squamous 

 cells and an elastic tunica 

 propria. They are sur- 

 rounded by striated muscle 



fibers, chiefly longitudinal. The lachrymal sac, which is provided with 

 small branched tubular glands, and the nasolachrymal duct, are lined 

 with two-rowed columnar epithelium and a lymphoid tunica propria, which 

 is separated from the underlying periosteum by a dense plexus of veins. 



FIG. 428. FROM A SECTION OP A HUMAN LACHRYMAL 

 GLAND. X 420. 



A, Gland body; a, tubule cut across; a', group of tubules cut 

 obliquely; s, intercalated tubule; s', intercalated tubule 

 in cross section; b, connective tissue. B, cross section of 

 an excretory duct; e, two-rowed cylindrical epithelium; 

 b, connective tissue. 



EAR. 



DEVELOPMENT AND GENERAL ANATOMY. 



The ear is divided into three parts: the external ear, including the 

 auricle which projects from the surface of the body, and the external 

 auditory meatus which is the passage leading to the tympanic membrane 

 or "drum"; the middle ear, including the tympanic cavity and the chain of 

 three bones extending across it; and the internal ear which is a system of 

 epithelial ducts in connection with the terminal branches of the acoustic 

 nerve, found imbedded in the temporal bone. 



The internal ear begins as a local thickening of the epidermal ecto- 

 derm near that portion of the medullary tube which later becomes the pons. 

 The thickened areas are invaginated as shown in Fig. 429 A and B, and 

 the pockets thus produced become separated from the epidermis in the 

 form of vesicles [otocysts]. From -near the center of the medial surface 



