88 THE KIDNEYS, BY C. LUDWIG. 



chief tubes of different medullary rays begin to coalesce, and 

 so on. The ultimate passages resulting from this paired mode 

 of union the so-called ductus papillares open ultimately on 

 the free surface of the papillae. As regards the diameter of 

 these canals, the general rule is, that every tubule resulting 

 from the junction of two is slightly wider than those which 

 coalesce to form it. 



2. COMBINATION OF THE TUBULES TO FOKM PRIMITIVE CONES. 

 A limited number of tubuli uriniferi stand in a more 

 intimate relation to each other than to any of the others. The 

 association of these is effected by the circumstance that the 

 collecting tubes of these groups run in one and the same 

 medullary ray, and ultimately open into one and the same 

 chief tube. The tubules that form the collecting tubes, how- 

 ever, even when they run separately, are so arranged that they 

 are easily recognized as belonging to the same group. All the 

 portions which belong to such a division preserve, when 

 regarded as a whole, somewhat of the appearance of a cone or 

 of a flask, the apex of which is in the papilla, and the base in 

 the cortex. As the kidneys, so far as regards the tubuli 

 uriniferi, are composed of an aggregate of many such primitive 

 cones, as they may be called, it is necessary in order to under- 

 stand the kidney to know their structure. In describing 

 them we shall commence from the papillary extremity of the 

 tubuli uriniferi, and pass towards the cortex. 



Each of the main or principal tubes, by the coalescence of 

 which the papillary ducts are formed, passes from within or 

 from just above the papilla to the middle of each medullary ray, 

 and having reached that point, speedily undergoes dichotomous 

 division into a number of branches : as far as we know, this 

 division occurs within a limited region of the medulla, so that 

 each collecting tube becomes independent at a short distance 

 above the papilla. The collecting tubes proceeding from each 

 principal tubule run all together in close approximation, and 

 nearly parallel to one another, as far as to the periphery of the 

 kidney, and form the stem of the fasciculus of tubules to 

 which the term " medullary ray " has been applied. Each 

 collecting tube remains unbranched until it has nearly arrived at 



