356 



MANUAL OF HISTOLOGY. 



e 



with clear, low, cylindrical cells, traversing the whole organ (fig. 348, 



a-d). We shall refer to this again. 



The ducts, or systems of ducts of racemose glands, however, are recog- 

 nised by all. The most simple forms in which 

 these may be seen are to be found in the small 

 glands of mucous membranes (fig. 349). Here 

 we see the vesicles making up a lobule, continued 

 into a shorter or longer passage of small diameter, 

 whose wall is formed by a prolongation of the mem- 

 brana propria. Among very small glands of this 

 nature the junction of two tubes, such as that just 

 described, may constitute the whole duct of the 

 organ (fig. 326). But in others the matter is not 

 so simple, and in the larger mucous glands the 

 common canal of exit from a group of lobules 

 formed by the confluence of their ducts is but a 

 branch of the true common passage, In the 

 latter, or even in a branch of the first order of 

 any considerable gland, we no longer find the 

 simple homogeneous structure of the membrana 

 propria ; the walls are here composed of longi- 

 tudinally arranged connective-tissue fibres, in 

 addition to which an external stratum of looser 

 texture may be remarked. They are lined, like- 

 wise, within with a layer of epithelium cells. 

 The length and breadth of these passages is sub- 

 ject to much variation. 



What has just been described may serve as a 

 key to the mode of formation of the larger arfd 

 even largest glands. The subdivision and rami- 

 fication of the passages in the latter has only 

 advanced further, and the groups of lobules 

 may be said to correspond to a certain extent to 

 the individual mucous glands. 



The further diversity of form of organs of this 

 kind depends, also, in a great measure on the 

 peculiar course of these passages. Thus, 'in the 

 pancreas we see the principal duct passing almost 



directly through the axis of the gland towards its apex. Many other 



organs, also, as, for instance, the lachrymal and mammary glands, are pos- 



Fig. 348. Fvom the kidney of 

 the Guinea-pig, in vertical 

 section, a-d, excretory ; and 

 e-h, secreting poi-tion of the 

 canal. 



Fig. 349. Small mucous glands, some of whose ducts unite in a 

 common outlet. 



sessed of several outlets : the union of the final twigs to form one common 

 canal may be said in this case not to have taken place. 



In regard to the texture, in these instances we have presented to us in 



