UNION OF URINARY TUBULES INTO PRIMITIVE CONES. 89 



the cortical extremity of the medullary ray. It here divides 

 into a number of branches of nearly equal size, each of which, 

 remaining isolated to its extremity, forms a urinary tubule. 



Each of these tubuli uriniferi proceeds in the form of a short 

 arch from the collecting tube, and with its intermediary 

 portion winds at the base of the cone, as far as to the surface 

 of the kidney, so that in penetrating from the fibrous capsule 

 into the substance of the organ we first meet with tortuous 

 canals, which chiefly consist of the windings of the interme- 

 diary portion. From this point the windings return again to 

 the axis of the cone (medullary ray), and, pursuing a straight 

 course, enter the spaces between the collecting tubes of the 

 medullary ray. Wherever in the course of this path the 

 canaliculi reach the medulla, the formation of the loops begins, 

 so that throughout the entire limiting or peripherical layer of 

 the medulla tubule after tubule loops in the manner described. 

 After having formed the loop, the ascending limb of each, as it 

 passes on towards the tortuous portion, still continues to lie in 

 juxta-position with its own fasciculus of collecting tubes, but 

 gradually separates from them, and forms the tortuous portion. 

 These last finally form a ring around the medullary ray in the 

 cortex, where this is not already invested as by a sheath with 

 the windings of the intermediary portion. 



3. COALITION OF THE PRIMITIVE CONES TO FORM THE 

 PYRAMIDS OR RENCULI. If the mode in which the main 

 canals of the primitive cones in the papilla coalesce to form 

 the ductus papillares be understood, the formation of a pyramid 

 from the association of numerous primitive cones will also 

 be intelligible. Two points only require special notice. The 

 first relates to the mode of origin of the lacuniform spaces of 

 the limiting layer of the medulla that are filled with blood- 

 vessels. These result from the circumstance that at the point 

 where the cortex ceases the medullary ray also suddenly loses 

 its sheath of cortical substance which has hitherto invested it. 

 The investment of the primitive cone thus forms there a deep 

 inflection like that of a flask, at the part where the belly is 

 continuous with the neck. If we now consider two or several 

 such flask-like bodies to be so arranged that their bellies and 



