CH. LI I.] 



OLFACTORY TRACT. 



711 



some auimals, like the frog, is provided with hairs. These cells, 

 which are called olfact^rial cells, are numerous, and the nuclei of 



Fig. 533. Nerves of the septum nasi, seen from the ri^ht side. . I, the olfactory bulb ; 

 i, the olfactory nerves passing through the foramina of the cribriform plate, and de- 

 scending to be distributed on the septum ; 2, the internal or septal twig of the nasal 

 branch of the ophthalmic nerve ; 3, naso-palatine nerves. (From Sappey, after Hirsch- 

 feld and LeveilU'.) 



the cells not being on the same level, a comparatively thick nuclear 



layer is the result (fig. 534, b). In the corium are a number of serous 



glands called Bowman's glands. They 



open upon the surface by fine ducts 



passing up between the epithelium 



cells. 



The distribution of the olfactory 

 nerves which penetrate the cribri- 

 form plate of the ethmoid bone and 

 pass to this region of the nasal mu- 

 cous membrane is shown in fig. 533. 

 The nerve-fibres are continuous with 

 the inner processes of the cells we 

 have termed olfactorial ; the columnar 

 cells between these act as supports to 

 them. 



The olfactory tract is an outgrowth 

 of the brain which was originally hol- 

 low, and remains so in many animals, 

 in man the cavity is obliterated, and 

 the centre is occupied by neuroglia : 

 outside this the white fibres lie, and 

 a thin superficial layer of neuroglia covers these. The three "roots" 

 of the olfactory tract have been traced to the uncinate gyrus mainly 



Fig. 



, 534. Semi-diagrammatic sec- 

 tion through the olfactory mu- 

 cous membrane of the new-born 

 child, n, non-nuclear; and /<. 

 nucleated portions of the epi- 

 thelium ; r, nerve's* ; iM, Bow- 

 man's glands. M. Schultze.) 



