THE HORSE. 



115 



medium of this serous investment have al- 

 ready been described. 



The albugineous tunic is fibrous, and 

 partly sub-serous. It forms a distinct cap- 

 sule, attached to the substance of the organ 

 by fibrous prolongations, which are in some 

 parts arranged in pits and depressions, so 

 as to mark out divisions on the surface of 

 the kidney. In addition to this, the albu- 

 sfineous coat surrounds the vessels and 

 ureter at the hilus, and enters the substance 

 of the organ. 



On cutting the kidney horizontally from 

 the convex to the concave border, there are 

 three different parts brought into view, to 

 be taken into consideration. Firstly, a 

 dark conteur, of about half an inch or more 

 in thickness, being generally less at the ex- 

 treme ends of the Iddney than at its middle, 

 which completely encircles the central part 

 of the gland, and is termed the cortical 

 sti'ucture, from its being most external. 

 This part of the kidney has somewhat a 

 granular aspect, and, when the vessels are 

 full of blood or injection, they appear more 

 or less arborescent, and clustered at innu- 

 merable minute but visible spots, to form 

 the Malpighian tufts. Next to this is a 

 lighter colored material, rather ash-colored, 

 but having a reddish hue, termed the me- 

 dullary substance. This term is not given 

 to it from the fact that it is medullary in 

 consistence, but used in the metaphorical 

 sense of being internally or centrally situ- 

 ated. 



Approaching still nearer to the concave 

 border of the kidney, is a funnel-shaped 

 cavity, with its apex towards the hilus, and 

 the base bounded by the medullary sub- 

 stance, which is the pelvis. The apex is 

 tubular, and continuous with the ureter, 

 of which the cavity is but an expansion. 



The walls of the cavity are lined by a 

 mucus membrane, which is loosely applied 

 to the medullary substance, and thrown 

 into folds, taking a radiated direction from 

 the mouth of the ureter. Opposite the 

 apex of the pelvis, the membrane is adher- 

 ent to a prominent border of the medullary 

 substance, concave from before backward, 



but convex from above downward, and is 

 pierced by foramina, into which the lining 

 membrane of the pelvis extends, so as to 

 form the uriniferous tubes. On dissecting 

 carefully away the mucus membranes of 

 the pelvis, we reach to the fibrous tunic, 

 which is not continuous on the medullary 

 ridge, but merely attached to its sides, so 

 as to increase the length of the boundaries 

 of the cavity. 



The ureter arising from this dilatation is 

 continuous outward toward the spine,^and 

 then backward, being related superiorly, 

 as it issues from the hillus, with the renal 

 vein ; and then crossing the posterior part 

 of the kidney at its inferior surface, it gets 

 betw^een the peritoneum and psoas muscles, 

 and is then traceable back to the bladder, 

 into which it opens. 



The renal arteries, one for each Iddney, 

 arise at almost right angles from the aorta, 

 after the latter has given off the anterior 

 mesenteric. The right one is more ante- 

 riorly situated, and is longer than the left 

 one. After each renal artery has given off 

 a branch or more to the supra-renal cap- 

 sule of the same side, it divides, on reach- 

 ing the hilus, into a variable number of 

 branches, usually eight or ten, which pierce 

 the kidney at different parts of the hilus, 

 whilst a few branches proceed along the 

 surface, supplying the capsule, and then 

 also piercing the organ. The arterial 

 branches entering the kidney have a de- 

 finite arrangement, forming a kind of arch 

 superiorly to the pelvis, from which second- 

 ary divisions emanate and pierce the organ 

 in all directions, so as to reach the cortical 

 substance, abruptly dividing into numer- 

 ous branches, which eventually subdivide 

 to form capillaries. By this it is evident 

 that the cortical substance is more vas- 

 cular than the medullary ; indeed the latter 

 is very scantily supplied with arterial 

 blood. 



From the arterial terminations the venous 

 origins occm-, and these unite to form 

 branches, having a similar arrangement as 

 the arteries ; only as they reach the pelvis, 

 almost opposite the apex, they meet to 



