The =kidneys= are relatively large, forming about ¹⁄₁₅₀ to ¹⁄₂₀₀ of the
body-weight; the weight of the kidney of a medium-sized dog is about two
ounces (ca. 50 to 60 grams). They are both bean-shaped, thick
dorso-ventrally, with a rounded ventral surface and a less convex dorsal
surface; the surfaces are smooth.
The =right kidney= (Fig. 343) is not subject to much variation in
position; it is situated usually under the last rib and the first three
lumbar transverse processes. Its anterior part lies in the deep renal
impression of the liver; its posterior part is related to the sublumbar
muscles dorsally, and the pancreas and duodenum ventrally.
The =left kidney= (Fig. 342) is subject to some variation in position;
this is due to the fact that it is loosely attached by the peritoneum,
and is affected by the degree of fullness of the stomach. When the
stomach is nearly empty, the kidney usually lies under the transverse
processes of the second, third, and fourth lumbar vertebræ, so that its
anterior pole is opposite to the hilus of the right kidney. As the
stomach fills it pushes the left kidney backward, so that the anterior
pole of the latter may be opposite the posterior pole of the right
kidney. The dorsal surface is related to the sublumbar muscles. The
ventral surface is in contact with the terminal part of the colon (Colon
descendens). The external border is related to the spleen and the flank.
The anterior extremity touches the stomach and the left extremity of the
pancreas.
The external border of the left kidney has considerable contact with
the flank, and hence it may be palpated more or less distinctly in the
living animal about half-way between the last rib and the crest of the
ilium.
=Structure.=—The hilus is in the middle of the inner border and is,
relatively wide. Cortex, limiting zone, and medulla are clearly defined.
On frontal sections it is seen that the medullary substance forms a
horizontal renal crest like that of the horse, but with the important
difference that curved ridges proceed dorsally and ventrally from the
crest somewhat like buttresses. Sections above or below the renal crest
often cut these ridges in such a manner as to give the appearance of
conical papillæ, and thus tend strongly to produce a false impression.
The pelvis is adapted to this arrangement of the medullary substance. It
incloses a central cavity into which the renal crest projects, and is
prolonged outward between the ridges, forming cavities for the latter,
thus simulating the appearance of calyces which do not exist.
The =ureters= present no special features.
The =bladder= is abdominal in position, the neck lying at the anterior
border of the pubic bones. It is relatively large, and when full, the
vertex may reach to the umbilicus. It has a practically complete
peritoneal coat.