614 



MANUAL OF HISTOLOGY. 



remind one of the follicles of Lieberkuhn. In the central portion of the 

 regio olfactoria they present themselves in great number, becoming more 

 scattered towards the edge, and finally disappearing. Their form is that 

 of an elongated tube, somewhat twisted below, and of varying calibre, 

 generally narrowing greatly at the mouth (d). Internally they are lined 

 with rather large gland-cells, containing usually a considerable quantity 

 of small yellow or brown pigment molecules, which fact explains, to a 

 certain extent, the peculiar tinge of the olfactory region. These glands 

 of JBoivman, whose existence was formerly erroneously denied, are to be 

 found in all the lower mammalia (2), and are not absent in man, although 

 they take the form here of a kind of transition to ordinary racemose 

 glands (Frey, Schultze). The secretion of Bowman 's glands, as regards its 

 composition and physiological significance, has not yet been made the 

 subject of investigation. 



Thus, we find the olfactory region in the lower mammals and human 

 infant (Schultze). In the adult, also, spots quite destitute of cilia are to 



Fig. 572. The olfactory region of the fox in vertical section (after Ecker). 

 B, columnar epithelium ; a, line of nuclei ; 6, of olfactory cells ; c, of pig- 

 mentary layer. A, adjacent ordinary ciliated epithelium ; e, boundary 

 between the two. C, ordinary racemose mucous gland. Z>, glands of 

 Bowman, with excretory ducts, d. E, a branch of the olfactory nerve; 

 /, ascending twig ramifying at g. 



be found, which vary, however, considerably in extent. But, under 

 certain circumstances,, the whole regio olfactoria has been observed to be 

 clothed with ciliated columnar cells (Geyenbaur, Leydig, and //. Mutter, 

 Welcker, Luschka, Henle, with Elilers). 



When we take into consideration the varying acuteness of the sense of 

 smell in different individuals, and also that frequently recurring catarrh 

 may induce changes of structure, this need not surprise us. 



At the border of the regio olfactoria the ordinary ciliated epithelium 

 gradually terminates (fig. 572 A), giving place to a no longer laminated 

 covering of long cylindrical cells (B). These (fig. 572, B ; 573, 1 a, 2 a) 

 dwindle down below .into thread-like processes, which descend into the 

 subjacent connective-tissue, where they become widened again, and under- 

 going division, unite by means of their branches with one another. In 

 this way a network of fibres, or rather of more or less homogeneous bands, 



