SPLANCHNOLOGY. 201 



substance forms the superficial lamina of the gland, is about two lines 

 thick, and sends long prolongations inwards between the membranous 

 fasciculi. A microscopical examination shows the cortex to be composed 

 of numerous arterial and venous ramifications, entangled with convoluted 

 uriniferous tubes (tubes of Ferrein); an immense number of small granules 

 may also be detected. These are the corpora or acini of Malpight. A 

 Malpighian corpus or corpuscle is a tuft of capillary arteries, arranged in 

 loops, close pressed together, and inclosed in a slight dilatation of the 

 urinary tube, which thus forms a capsule to it. A small artery called vas 

 inferens pierces this capsule, and then divides into the branches which are 

 coiled up to form this minute vascular ball, from the interior of which a 

 small vein {vas efferens) proceeds, smaller than the artery, and piercing the 

 capsule close to it, enters the venous plexus surrounding the convoluted 

 uriniferous tubes, and from which the blood is ultimately conveyed out of 

 the kidneys by the renal or emulgent vein. We have thus two distinct 

 systems of capillary vessels, through both of which the blood passes in its 

 course from the arteries to the veins. The first is an arterial capillary 

 system, forming the Malpighian tufts, contained within the uriniferous 

 tubes; the second is the venous plexus which surrounds these convoluted 

 tubes. It has been suf)posed that the former serve to liberate water and 

 the more simple elements of the blood, while the latter eliminate the more 

 complex urea, uric acid, &c. 



The tubular substance is internal to the cortex, and consists of fine vessels 

 arranged in about fifteen pyramids ; the bases directed outwards, the apices 

 towards the hilum. At and near the apex these vessels are straight, but, 

 proceeding outwaixls, they communicate ; and, on entering the cortical sub- 

 stance, become twisted and convoluted in the most complicated manner. 



The papillcPi or the mammillary processes^ form the apices of the cones. 

 Each is perforated by a number of fine holes, the orifices of the individual 

 tubes, and through which the urine flows when these are compressed. The 

 extremities of the papillae are embraced by the calyces^ membranous cups 

 which unite with each other at the other end to form the ureter. Those 

 calyces of each extremity, as well as those in the centre, unite into the three 

 small tubes, the infundibula^ which, after a short course, terminate in the 

 pelvis, an oval flattened reservoir, which is continued into the ureter. 



2. The Ureter is the excretory duct of the kidney, and extends to the 

 urinary bladder. Each ureter is about eighteen inches long, and of the 

 thickness of a goose-quill. They enter the bladder by passing obliquely 

 between its muscular and mucous coats. 



Attached to the upper extremity of each kidney is a small gland-like 

 body, termed renal cajjsuk, or supra-renal body. They are well supplied 

 with vessels, but do not appear to be especially connected with the kidneys. 

 Their use is unknown, although it is probable that with the thymus and 

 thyroid bodies they are concerned most especially in the economy of the 

 foetus. 



3. The Bladder, vesica urinaria, is the reservoir of the urine, which con- 

 stantly trickles into it from the ureters. It lies behind the pubes, and rests 



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