GLAND. 



(See the biliary organs of 

 Mdiitnitl iui 1'ulgar'ni, fifi. 38, 

 vol. i. p. 111.) 



In tlit liver of Mammalia 

 and Man, both in the embryo 

 and after birth, it is much 

 more difficult to demonstrate 

 the ultimate tubes with their 

 cojcal extremities; indeed the 

 existence of such canals is ra- 

 ther deduced from the ana- 

 logy of the liver in the lower 

 animals than from actual ob- 

 servation. Miiller states that 

 the blind free extremities of 

 the biliary ducts are visible 

 on the surface of the liver 

 with the microscope in the 

 embryo of Mammalia; but 

 that owing to their compact 

 arrangement they are less dis- 

 tinct than in birds, so that 

 their internal connexions can- 

 not be perceived.* In a few 

 Mammalia, however, as the 

 squirrel, (sciurus ntl^aris,) he 

 i '1 .served with the microscope 

 the blind cylindrical extremi- 

 ties of the biliary ducts on 

 the surface of the liver, pre- 

 senting a branching and foliaceous appearance. 



g. 217.) The exact mode of termination of 



Fig. 217. 



485 



Fig. 216. 



. 218. 



the biliary tubuli was still more distinctly seen 

 in a portion of liver considerably magnified, 

 taken from an embryo of the quail, ( Tetrao 

 futiirnijc,) about one inch long (Jig. 218J. 

 From the published 

 account of Mr. 

 Kiernan's valuable 

 observations on the 

 minute structure of 

 the liver, it does 

 not apjiear that the 

 actual terminations 

 of the biliary tubes 





I-. r. p. BO, 



in blind extremities were perceived, although 

 that such is their disposition is rendered very 

 probable from what was seen with the mi- 

 croscope, and especially because it was found 

 that much greater difficulty was experi- 

 enced in injecting these tubes than the 

 bloodvessels, on account, as it was sur- 

 mised, of the bile contained within them 

 having no exit.* 



Lastly, in tracing the minute texture 

 of these complex glands of the Mam- 

 malia, it is necessary to call the attention 

 of the reader to a circumstance which of 

 all others has been the most fertile source 

 of error, so much so indeed as to have 

 misled the great majority of anatomists. 

 It is this : in many glands small rounded 

 or berry-shaped corpuscles seem to be 

 appended to the commencement of the 

 secreting tubes, so that a deceptive ap- 

 pearance is produced, as if cells or little 

 bags were placed between the terminal 

 bloodvessels and the small excretory 

 ducts. This appearance of cells or even 

 . of solid rounded corpuscles is depen- 

 dent on two causes : in some glands the se- 

 creting canals are so coiled up that, as is seen 

 in the human testis, when a section is made in 

 the uninjected state an apparently granular tex- 

 ture is presented, (Jig. 219;) but a second 

 influential circumstance is that in many in- 

 stances each of the secreting tubes swells out 

 at its ccBcal end into a slightly enlarged cul- 

 de-sac (ptdvnmdattd tubes), so that when they 

 are viewed in an aggregate form, the semblance 

 of roundish-shaped granules is seen, (Jig. 

 220.) As these and all other varieties which 

 are presented in the glandular formation are 



* Phil. Trans. IBM. p. 741. 



