Mr. Beale on the Anatomy of the Liver of Vertebrate Animals. 473 



The secreting cells appear to occupy the entire cavity of the tube, 

 and are not arranged in any order ; so that the secretion, having 

 escaped from the cells, must pass off towards the duct by the slight 

 interstices between them. A similar disposition of the secreting 

 epithelial cells occurs, but in a less remarkable degree, in some other 

 glands ; as the pancreas, lacteal, sebaceous, and sweat glands. 



The conclusions to which the author has arrived may be summed 

 up as follows : — • 



1. That the liver of vertebrate animals essentially consists of two 

 solid tubular networks mutually adapted to each other. One of 

 these networks contains the liver-cells, and the other the blood. 



2. The cell-containing network is continuous with the ducts. 

 The small delicate epithelial cells lining the latter channels contrast 

 remarkably with the large secreting cells, which are not arranged 

 in any definite manner within the tubes of the network. 



3. The duct is many times narrower than the tubular network at 

 the point where it becomes continuous with it. 



4. Injection passes sometimes on one, and sometimes on the other 

 aide of the tube, or between the cells, when two or more lie across 

 the tube. Often, a cell becomes completely surrounded with in- 

 jection. As injection can thus be made to pass readily //-om the 

 ducts into the network and around the cells, it follows that there 

 can be no obstacle to the passage of the bile along the same chan- 

 nels in the opposite (its natural) direction. 



5. In some animals, the most minute ducts are directly connected 

 with the tubes of the cell-containing network ; of these branches, 

 some pass amongst the most superficial meshes to join the network 

 at a deeper part. In other animals the finest ducts first form a net- 

 work which is continuous with that containing the liver-cells. 



6. The interlobular ducts do not anastomose, but the branches 

 coming off from the trunk are often connected with each other, as 

 well as with the parent trunk, near their origin from it. 



7. The walls of the smallest ducts are composed of basement 

 membrane only. The thick complex coat of the larger ducts con- 

 tains within it small cavities (the so-called glands of the ducts), by 

 means of which the bile in these ducts would be brought into close 

 proximity with the arteries, veins and lymphatics, which are very 

 abundant wherever the ducts ramify. 



8. The office of the vasa aberrantia, which are so numerous in 

 the transverse fissure of the human liver and in the larger portal 

 canals, appears to be similar to that of the cavities in the walls of 

 the ducts. It is worthy of remrak, that the network of vessels 

 ramifying so abundantly in the coats of the gall-bladder, in the 

 transverse fissure, and in the larger portal canals, are arranged in a 

 similar manner, each branch of artery being accompanied by two 

 branches of the vein. 



9. The liver is therefore a true gland, consisting of a formative 

 portion and a system of excretory ducts directly continuous with it. 

 The secreting cells lie within a delicate tubular network of base- 

 ment membrane, through the thin walls of which they draw from 

 the blood the materials of their secretion. 



PhiL May. S. 4. Vol. 11. No. 74. June 1856. 2 I 



