1130 



THE URINARY ORGANS. 



mous epithelial cells which are reflected from the lining membrane on to the 

 glomerulus at the point of entrance or exit of the afferent and efferent vessels. 

 The whole surface of the glomerulus is covered with a continuous layer of the 

 same cells on a delicate supporting membrane, which with the cells dips in between 

 the lobules of the glomerulus, closely surrounding them (Fig. 719). Thus, between 

 the glomerulus and the capsule a space is left, forming a cavity lined by a con- 



FIG. 718. Minute structure of kidney. 



1 IG. 719. Malpighian body. 



tinuous layer of cells, which varies in size according to the state of secretion and 

 the amount of fluid present in it. The cells are squamous or flattened. 



The tubuli uriniferi, commencing in the Malpighian bodies, in their course 

 present many changes in shape and direction, and are contained partly in the 

 medullary and partly in the cortical portions of the organ. At their junction with 

 the Malpighian capsule they present a somewhat constricted portion which is 

 termed the neck. Beyond this the tube becomes convoluted, and pursues a con- 

 siderable course in the cortical structure, constituting the proximal convoluted 

 tube. After a time the convolutions disappear, and the tube approaches the 

 medullary portion of the kidney in a more or less spiral manner. This section of 

 the tube has been called the spiral tube of Schaclioiva. Throughout this portion 

 of their course the tubuli uriniferi have been contained entirely in the cortical 

 structure, and have presented a pretty uniform calibre. They now enter the 

 medullary portion, and suddenly become much smaller, quite straight in direction, 

 and dip down for a variable depth into the pyramids, constituting the descending 

 limb of Henle's loop. Bending on themselves, they form a kind of loop, the loop 

 of ffenle, and, reascending, become suddenly enlarged and again spiral in 

 direction, forming the ascending limb of Henle's loop, and re-enter the cortical 

 structure. This portion of the tube does not present a uniform calibre, but 

 becomes narrower as it ascends and irregular in outline. As a narrow tube it now 

 is found in the cortex along the medullary ray and ascends for a short distance, 

 when it again becomes dilated, irregular, and angular, and leaves the medullary 

 ray to enter the labyrinth of the cortex. This section is termed the irregular 

 tubule, ; it terminates in a convoluted tube which exactly resembles the proximal 

 convoluted tubule, and is called the distal convoluted tubule. This again terminates 

 in a narrow curved or junctional tube, which enters the straight or collecting tube. 



Each straight, otherwise called a collecting or receiving, tube commences by a 

 small orifice on the summit of one of the papillae, thus opening and discharging 

 its contents into the interior of one of the calices. Traced into the substance of 

 the pyramid, these tubes are found to run from apex to base, dividing dichotomously 

 in their course and slightly diverging from each other. Thus dividing and sub- 

 dividing, they reach the base of the pyramid, and enter the cortical structure 

 greatly increased in number. Upon entering the cortical portion they continue a 

 straight course for a variable distance, and are arranged in groups called medullary 

 rays, several of these groups corresponding to a single pyramid. The tubes in the 



