988 THE URINARY ORGANS. 



bodies, which are small rounded masses, varying in size, but average about y-Lg- of 

 an inch in diameter. They are of a deep-red color, and are found only in the cor- 

 tical portion of the kidney. Each of these little bodies is composed of two parts 

 a central glomerulus of vessels, called a Malpighian tuft, and a membranous en- 

 velope, the Malpighian capsule, or capsule of Bowman, which latter is a small 

 pouch-like commencement of a uriniferous tubule. 



The Malpighian tuft, or vascular glomerulus, is a network of convoluted 

 capillary blood-vessels held together by scanty connective tissue and grouped into 

 from two to five lobules. This capillary network is derived from a small arterial 

 twig, the afferent vessel, which pierces the wall of the capsule, generally at a point 

 opposite that at which the latter is connected with the tube ; and the resulting 

 vein, the efferent vessel, emerges from the capsule at the same point. The afferent 

 vessel is usually the larger of the two (Fig. 545). The Malpighian or Bowman s 

 capsule, which surrounds the glomerulus, is formed of a hyaline membrane sup- 

 ported by a small amount of connective tissue which is continuous with the con- 

 nective tissue of the tube. It is lined on its inner surface by a layer of squa- 

 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. 546). Thus, between 

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



FIG. 515. Minute structure of kidney. FIG. 546. 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, as above stated, are squamous in the 

 adult, but in the foetus and young subject they are polyhedral or even columnar. 



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 8chachowa. 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 Henles loop. Bending on themselves, they form a kind of loop, the loop 

 f>f Henle, and, reascending, become suddenly enlarged and again spiral in 

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



