_L_, Lobes of cortex; _P_, papillæ; _C_, calyx major; _c′_, calyces
minores.
]
The kidneys are embedded in a large amount of perirenal fat. The weight
of a kidney is about 20 to 25 ounces (ca. 570 to 700 gm.), the left one
being usually an ounce or more the heavier. The two form about ¼ per
cent. of the body-weight.
The right kidney measures about 8 to 10 inches (ca. 20 to 25 cm.) in
length, 4 to 5 inches (ca. 10 to 12 cm.) in width, and 2½ to 3 inches
(ca. 7 cm.) in thickness. The left kidney is one or two inches (ca. 2
to 5 cm.) shorter, but its posterior part is much thicker than the
right one.
=Structure.=—The hilus is equivalent to the hilus and sinus of the
kidney of the horse; in the right kidney it is an extensive elliptical
cavity, in the left, a deep fissure. The pelvis is absent. The ureter
begins at the junction of two wide, thin-walled tubes, the =calyces
majores=; the anterior calyx is usually the larger. Each calyx major
gives off a number of branches, and these divide into several
funnel-shaped =calyces minores=, each of which embraces a renal papilla.
The space not occupied by the calyces and vessels is filled with fat.
On section through the kidney the =renal pyramids= are easily made out.
The blunt apex of each pyramid, the =papilla renalis=, projects into a
calyx minor. On each papilla are small orifices (Foramina papillaria) by
which the terminal renal tubules (Ductus papillares) open into the
calyx. The renal columns are much more distinct than in the horse.
At the hilus the renal artery is dorsal, the vein in the middle, and the
ureter ventral; a quantity of fat surrounds these structures in the
hilus.
The kidneys of the =sheep= are bean-shaped and smooth, without any
superficial lobation. The soft organ is regularly elliptical in form,
with convex dorsal and ventral surfaces and rounded extremities; its
length is about 2½ to 3 inches (ca. 5 to 8 cm.), its width about 1½ to 2
inches (ca. 4 to 5 cm.), and its thickness a little more than 1 inch
(ca. 3 cm.). In position they resemble those of the ox, except that the
right one is usually a little further back, and lies under the first
three lumbar transverse processes. The average weight of each is about
four ounces. The hilus is in the middle of the inner border. There is a
renal crest or common papilla formed by the fusion of twelve to sixteen
pyramids.
[Illustration: