THE XOSK. 387 



ducts open into the posterior nares, the remainder on the mucous 

 membrane of the pharvngo-oral cavity at two symmetrically placed 

 points (Fig. 238 R). 



(5) The lachrymal duct (see p. 428) opens into the nasal cavity 

 at the point where the lateral sinus opens into the external chamber 

 of the superior nasal sinus. 



(6) [The glands of Bowman (Fig 1 . 240 I) are freely distri- 

 buted in the nasal mucous membrane. Each gland is usually 

 rounded or flask-shaped, and consists of a single layer of large epi- 

 thelial cells possessing distinct nuclei and nucleoli. The epithelium 

 of the glands possesses no basement membrane (M. Schultze and 

 Hoffmann 1 ), but is bounded externally by a layer of nerve-fibres 

 and connective-tissue. 



The glands situated more superficially have straight ducts open- 

 ing on the surface; those placed more deeply have usually curved 

 ducts (Paschutin).] 



d. The mucous membrane of the nasal cavities. That part of 

 the superior sinus immediately around the anterior naris is lined 

 with stratified epithelium ; the rest of the nasal cavity is lined with 

 columnar ciliated epithelium. The epithelial layer rests on a sub- 

 epithelial network, and this again on a submucous connective- 

 tissue layer possessing numerous vessels and nerves. 



(i) The epithelial layer (Fig. 241) consists of columnar cells, 

 which in the olfactory region are of two kinds ; in other regions the 

 epithelium consists of closely-applied ciliated, thick cells, possessing 

 large oval nuclei, and having irregular, branched bases or 'feet.' 

 The cells are 0-032-0-048 mm. long; the nuclei 0-016-0-018 mm, 

 long, and o - oo6 0*008 mm. broad. The free borders of the cells 

 bear a number of fine cilia. 



In the olfactory region a second set of cells, olfactory cells, are met 

 with ; these cells (Fig. 241 II) possess each an oval body, enclosing 

 a large nucleus, and a peripheral and central process. The peripheral 

 processes reach to the general surface of the surrounding epithelium 

 and there terminate in a number (5-8) of stiff cilia ; these cilia are 

 sometimes 0-09 mm. long, they are thicker at their bases than the 

 ordinary cilia (Schultze) ; according to Hoffmann, a second system of 

 stiffer and longer cilia is met with ; of which each olfactory cell 

 possesses as a rule only one. The bodies of the olfactory cells are 

 0-009-0-010 mm. long, and 0-007-0-008 mm. broad; the peripheral 



1 Paschutin describes a basement membrane. 

 C C 2 



