ABDOMINAL VISCERA OF THE HORSE. 77 
& 
extreme ends of the kidney than at its middle, which completely 
encircles the central part of the gland, and is termed the cortical 
structure, 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 innumerable minute but visible spots, to form the 
Malpighian tufts. Next to this is a lighter coloured material, 
rather ash-coloured, but having a reddish hue, termed the 
medullary 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 situated. 
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 substance, 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 mucous 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 
adherent to a prominent border of the medullary substance, 
concave from before backwards, but convex from above down¬ 
wards, and is pierced by foramina, into which the lining mem¬ 
brane of the pelvis extends, so as to form the uriniferous tubes. 
On dissecting carefully away the mucous 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 outwards 
towards the spine, and then backwards, being related superiorly, 
as it issues from the hilus, with the renal vein, and then 
crossing the posterior part of the kidney at its inferior surface, 
it gets between the peritoneum and psoas muscles, and is then 
traceable back to the bladder, into which it opens. 
The renal arteries, one for each kidney, arise at almost right 
angles from the aorta, after the latter has given off the anterior 
mesenteric. The right one is more anteriorly situated, and is 
longer than the left one. After each renal artery has given off 
a branch or more to the supra-renal capsule of the same side, it 
divides, on reaching 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 definite arrange¬ 
ment, forming a kind of arch superiorly to the pelvis, from 
which secondary divisions emanate and pierce the organ in 
