242 



REN. 



from the basement membrane which it lines, 

 and to fall into and block up its narrow 

 channel." It consequently happens that, in 

 face of mechanical obstacles such as those 

 above mentioned, the force employed to in- 

 ject the tubes sooner or later bursts their 

 coats ere their extremities have been reached.* 

 Course and Termination of the Tabes. Tra- 

 cing the tubes from the apex of a medullary 

 cone, on the surface of which their open 

 mouths may be seen, we find them taking a 

 straight course through the pyramid, branch- 

 ing dichotomously and diverging as they pro- 

 ceed (j#g. 143). After reaching the base of the 

 pyramid, their course through the cortical 

 portion is very various ; many tubes imme- 

 diately take a very tortuous course, some of 

 them bending down into the inter-pyramidal 

 portions of the cortical substance, while those 

 near the centre of the pyramid pass onwards 

 in a mass and in a straight line towards the 

 surface, the tubes on the sides of the bundle in 

 their progress passing off successively in a tor- 

 tuous course through the cortical substance, 

 so that only a few of the central tubes in 

 each bundle retain their straight course quite 

 up to the surface of the kidney ; these finally 

 turn backwards, making many convolutions 

 in the cortical substance. After leaving the 

 medullary cones, the branching of the tubes, 

 except in very rare instances, appears to cease ; 

 occasionally two tubes in the cortical sub- 

 stance unite in passing towards the cones ; and 

 I once saw this occur at a very short distance 

 below the Malpighian bodies, so that two 

 short tubes, each with a Malpighian body at 

 its extremity, united into one common tube. 

 Some distinguished anatomists have main- 

 tained that the tubes, after dividing in the corti- 

 cal substance, reunite in a plexiform manner, 

 and they have described this as their natural 



* In opposition to the opinion of Mr. Bowman, 

 supported as it is by facts and arguments which, to 

 most practical anatomists who are acquainted with 

 the structure and relations of the tubes and Mal- 

 pighian bodies, will appear quite conclusive, Mr. 

 Toynbee states that the possibility of injecting the 

 entire length of the tubes, and even the Malpighian 

 capsules from the pelvis of the kidney, is abundantly 

 proved by many of his own specimens, in which the 

 Malpighian bodies are in this way distended, and 

 that without any extravasation into the vascular 

 tissues. If the account which Mr. Bowman has 

 given of the connexion -of the tubes with the Mal- 

 pighian bodies be a correct one, it is clearly impos- 

 sible that the tubes, long, tortuous, closed at their 

 extremities, and always containing more or less 

 liquid, can be completely injected from the pelvis of 

 the kidney, unless the rupture of the tube or of the 

 Malpighian capsule allows the liquid contents of the 

 tube to give place to the injected material. Cer- 

 tainly the Malpighian capsules cannot possibly be 

 injected from the tubes so long as the tubes and the 

 capsules remain entire. If, therefore, Mr. Toynbee 

 is correct in his observation on this point, the ex- 



flanation of the fact must, as I think, be that which 

 have given. His account of the Malpighian bo- 

 dies (Med. Chir. Transactions, vol. xxix. p. 311), 

 and of their relation to the tubes, so far as I can 

 comprehend the description given, appears to be 

 incorrect ; and his diagrams of these bodies (Plate 8, 

 loc. cit.) represent appearances such as I have never 

 observed in the course of my own examinations. 



mode of termination. This opinion is in all 

 probability founded on deceptive appearances, 

 such as must often have presented themselves 

 when the means of observation jyere less per- 

 fect than they now are, and which even at this 

 time are but of too frequent occurrence. It 

 appears to be a general fact that the tubes 

 divide in their course from the apices of the 

 medullary cones towards their opposite termina- 

 tions, but they never reunite while passing in 

 this direction. Other anatomists have con- 

 sidered the tubes to terminate in free blind 

 extremities unconnected with the Malpighian 

 bodies ; and they have based their opinion on 

 the appearances of injected specimens as well 

 as on those of recent ones. With reference 

 to this question Mr. Bowman* remarks, " As 

 the injection always stops short of the real 

 extremities of the tubes, it must necessarily 

 show apparent free extremities and others 

 may be produced by the section requisite for 

 the examination of the part. As for the false 

 appearances presented by recent specimens, 

 they are obviously referable to the sudden 

 bending down of a tube behind the part 

 turned to the observer. In a mass composed 

 of convolutions, many such must continually 

 occur ; and their real nature may be easily 

 determined by the use of a high power and 

 varying focus." In addition to the sources of 

 fallacy thus alluded to by Mr. Bowman, there 

 is another, to which I have already referred-]- 

 in describing the fibrous matrix in which the 

 tubes are packed. To an inexperienced obser- 

 ver, few appearances could be more deceptive 

 than the apparent abrupt terminations of the 

 tubes, as these are seen in the spaces formed 

 by the surrounding tissue, here visible in the 

 meshes of the network, and there suddenly 

 concealed as they pass beneath the fibrous 

 tissue. 



The manner in which the tubes actually 

 terminate is by becoming continuous with the 

 Malpighian bodies. This fact, which can be 

 demonstrated in many of the tubes, is a matter 

 of fair inference and of moral certainty in the 

 case of every tube. The proofs of this fact, 

 and the precise mode of continuity, we shall 

 presently proceed to examine. 



Structure of the Tubes. The uriniferous 

 tubes contain the two structures which usu- 

 ally compose the mucous tissue, viz. the 

 basement membrane and the epithelium.^ 



The basement membrane is a thin transpa- 

 rent homogeneous lamina, simple and entire, 

 without any aperture or appearance of struc- 

 ture. It forms the parenchymal wall of the 

 uriniferous tubes ; gives them their form, size, 

 and stability ; is in relation, on the one hand, 

 with the vascular system of the organ and the 

 investing fibrous matrix, and on the other, 

 with the epithelial lining of the tubes. The 

 epithelium adheres to the inner surface of the 

 membrane by organic union : it sometimes 

 separates readily after maceration in water, 

 and in some forms of chronic inflammation of 



* Loc. cit. 



f Vide ante, p. 239. 



Vide art. Mucous MEMBRANE. 



