486 



GLAND. 



Fig. 219. considered in the 



several articles 

 on the individual 

 glands, it is only 

 necessary to state 

 in this place that 

 what are called 

 indifferently lu- 

 bules, glandular 

 grains, vesicles, 

 acini, &c. are in 

 every instance 

 composed simply 

 of the secreting 

 canals variously disposed and arranged 



It is, however, very remarkable that whilst 

 those glands which arise from the alimentary 

 canal present an immense variety in the ar- 

 rangement of their secreting texture, the essen- 

 tial glands of the genito-urinary apparatus, the 

 kidney and the testicle, have a most uniform 

 structure, consisting of serpentine tubes of the 

 same diameter throughout their whole extent. 



The details into which I have thought it re- 

 quisite to enter prove that the true secreting 

 structure consists in every gland of nothing 

 else than a vascular membrane, on the surface 

 of which the glandular fluid is poured out; and 

 consequently that in those complex organs, as 

 the liver or kidney, in which the vascular se- 



Fig. 220. 



Peri^iheral ramijifation of the parotid diift, with some (if the vesicular terminations, 

 mtiynijicd = 1 10.* 



creting membrane is, for the sake of conveni- 

 ence, disposed in the form of extensively rami- 

 fied tubes, it is most important to recollect that 

 the glandular fluid is poured not only into the 

 ccecal extremity or commencement of each 

 tube, as is the commonly received opinion, but 

 along the whole extent of' the tube. For the 

 establishment of this fact, certainly the most 

 imjjortant in the history of the glands, we are 

 principally indebted to Professor Miiller. 



Excretory duct. Although the essential seat 

 of the glandular function is now ascertained, 

 some difficulty exists in determining the actual 

 extent of the secreting surface in the various 

 organs ; or in other words, at what precise 

 point the mucous canals ceasing to secrete, 

 become mere excretory passages/)- An attempt 

 to decide this point is, however, necessary, 

 because until this time the majority of anato- 



* Bcrres, 1. c. pt. 5, tab. ix. fig. 2. 



t I allude here of course to the peculiar secre- 

 tions, as (he bile, urine, inilk, &c. and not to ihe 

 secretion of mucus, which we know is poured out 

 along the whole extent of the excretory ducts. 



mists have signified by the term excretory duct, 

 not only the canals which simply bear away 

 the secreted fluid, but likewise those tubes 

 which constitute the true secreting apparatus, 

 and which, it is evident, are at the same time 

 both secreting and excreting canals, as they not 

 only secrete, but likewise carry to the larger 

 and non-secreting ducts the fluids poured out 

 by their parietes. 



In the simple sacculi or follicles, it is evi- 

 dent that the secreting structure is co-equal 

 with the extent of the bag itself, so that the 

 little orifice becomes the excretory duct; in the 

 tonsils, prostate, &c. there are several such 

 orifices or ducts. But at what point does 

 secretion cease in the compound glands ? Mr. 

 Kiernan states,* that in the liver the secreting 

 portion of the organ is confined to what he 

 calls the lobular biliary plexuses, or to those 

 tubes which are placed within the lobules; so 

 that here the excretory apparatus is very com- 

 plex, consisting of the interlobular tubes, those 



Phil. Trans. 1833, p. 741. 



