726 URINARY ORGANS. 



become convoluted, and anastomose freely with each other ; they are sometimes 

 called the tubes of Ferrein. At the bases of the pyramids, the straight tubes are 

 described as being collected into small conical bundles, the tortuous tubuli cor- 

 responding to which are prolonged upwards into the cortical portion of the kidney 

 as far as the surface, forming a number of small conical masses, which are named 

 the pyramids of Ferrein, several of which correspond to each medullary cone and 

 its corresponding portion of cortical substance. According to Mr. Bowman, the 

 tubuli uriniferi commence in the cortical substance as small, dilated, membranous 

 capsules, the capsules of the Malpighian bodies ; they also form loops, either by the 

 junction of adjacent tubes, or, according to Toynbee, by the union of two branches 

 proceeding from the same tube ; they have also been seen to arise by free closed 

 extremities. 



The Malpighian bodies are found only in the cortical substance of the kidney. 

 They are small round bodies, of a deep red color, and of the average diameter 

 of the -jltf of an inch. Each body is composed of a vascular tuft inclosed in a 

 thin membranous capsule, the dilated commencement of a uriniferous tubule. The 

 vascular tuft consists of the ramifications Of a minute artery, the afferent vessel, 

 which, after piercing the capsule, divides, in a radiated manner, into several 

 branches, which ultimately terminate in a finer set of capillary vessels. From 

 these, a small vein, the efferent, vessel, proceeds ; this pierces the capsule near the 

 artery, and forms a close venous plexus, with the efferent vessels from other 

 Malpighian bodies, round the adjacent tubuli. 



The capsular dilatation of the Malpighian body is not always placed at the 

 commencement of the tube ; it may occupy one side (Gerlach) : hence their sub- 

 division into lateral or terminal. The membrane composing it is thicker than that 

 of the tubule ; the epithelium lining its inner surface is thin, and, in the frog, 

 provided with cilia3 at the neck of the dilated portion ; but in the human subject, 

 cilia? have not been detected. According to Mr. Bowman, the surface of the 

 vascular tuft lies free and uncovered in the interior of its capsule ; but, according 

 to Gerlach, it is covered with a thick layer of nucleated cells, similar to those 

 lining the inner surface of the capsule. 



Ducts. The ureter, as it approaches the hilus, becomes dilated into a funnel- 

 shaped membranous sac, the pelvis. It then enters the sinus, and subdivides 

 usually into three prolongations, the infundibula, one placed at each extremity, 

 and one in the middle of the organ ; these subdivide into from seven to thirteen 

 smaller tubes, the calyces, each of which embraces, like a cup-like pouch or calyx, 

 the base of one of the papillae. Sometimes, a calyx incloses two or more papillas. 

 The ureter, the pelvis, and the calyces consist of three coats, fibrous, muscular, 

 and mucous. 



The external or fibro- elastic coat is continuous, round the bases of the papillae, 

 with the tunica propria investing the surface of the organ. 



The muscular coat is placed between the fibrous and mucous coats. It consists 

 of an external or longitudinal, and an internal or circular stratum. 



The internal or mucous coat invests the papillae of the kidney, and is continued 

 into the orifices upon their surfaces. It is lined by epithelium of the spheroidal 

 kind. 



Vessels, and Nerves. The renal artery is large in proportion to the size of 

 the organ which it supplies. Each vessel divides into four or five branches, 

 which enter the hilus, and are invested by sheaths derived from the fibrous capsule ; 

 they penetrate the substance of the organ between the papillos, and enter the 

 cortical substance in the intervals between the medullary cones, dividing and 

 subdividing in their course towards the bases of the pyramids, where they form 

 arches by their anastomoses ; from these arches, numerous vessels are distributed 

 to the cortical substance, some of which enter the Malpighian corpuscles, whilst 

 others form a capillary network round the uriniferous tubes. 



The veins of the kidney commence upon the surface of the organ, where they 

 have a stellate arrangement ; they pass inwards, and open into larger veins, which 



