CH. LIIL] 



THE OLFACTORY APPARATUS 



735 



The distribution of the olfactory nerves which penetrate the 

 cribriform plate of the ethmoid bone and pass to this region of the 



FIG. 536. Nerves of the septum nasi, seen from the right side, $, I, The olfactory bulb; ], the 

 olfactory nerves passing through the foramina of the cribriform plate, and descending to be distri- 

 buted on the septum ; 2, the internal or septal twig of the nasal branch of the ophthalmic nerve ; 3, 

 naso-palatine nerves. (From Sappey, after Hirschfeld and Leveill<5.) 



nasal mucous membrane is shown in fig. 536. 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 hollow, and 

 remains so in many animals ; in man the 

 cavity is obliterated, and the centre is occu- 

 pied 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 and hippocampal regions 

 of the same side of the brain, which is the 

 portion experimentally found to be associ- 

 ated with the reception of olfactory impulses 

 (see p. 690). From the cells of the grey 

 matter here fibres pass by a complex path 

 to the corresponding regions of the opposite 

 side. There is also a communication via 

 the corpora mammillaria with the optic 

 thalamus and tegmentum of the mid-brain. 



The olfactory bulb has a more complicated structure ; above there 

 is first a continuation of the olfactory tract (white fibres enclosing 



FIG. 537. Semi - diagrammatic 

 section through the olfactory 

 mucous membrane of the new- 

 born child, o, Non-nuclear; 

 and b, nucleated portions of the 

 epithelium ; c, nerves ; dd-, Bow- 

 man's glands. (M. Schultze.) 



