192 URINARY ORGANS. 



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 cor- 

 tical 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 T^th 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 

 subdivision 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 cilia 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 hilum, becomes dilated into a funnel- 

 shaped membranous sac, t\\Q 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 ealices, each of which embraces the base of one of the papilla 1 . 

 Sometimes, a calix incloses two or more papilla?. The ureter, the pelvis, and 

 the ealices consist of three coats : fibrous, muscular, and mucous. 



The external or fibro-elaatic coat is continuous, round the bases of the papilla3, 

 with the tunica propria investing the surface of the organ. 



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

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



The internal or mucous coat invests the papilla? 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 hilum, and are invested by sheaths derived from the fibrous capsule; 

 they penetrate the substance of the organ between the papilla?, 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 unite into arches round the bases of the medullary cones. After receiv- 

 ing the venous plexus from the tubular portion, they accompany the branches 

 of the arteries of the sinus of the kidney, where they finally unite to form a 

 single vein, which terminates in the inferior vena cava. 



