The adrenal glands or suprarenal capsules are two conical bodies,
flattened from before backward, resting on the upper poles of the
kidneys close to the sides of the vertebral column; each has an anterior
and posterior surface and a concave base which is in contact with the
kidney. When viewed from in front the right gland is triangular and the
left crescentic. On the anterior surface there is a transverse sulcus or
hilum from which a large vein emerges. The arteries are less constant in
their points of entry, and are derived from three sources, the phrenic,
the abdominal aorta and the renal arteries. The glands are entirely
retro-peritoneal, though the right one, even on its anterior surface, is
very little covered by peritoneum. In a vertical transverse section each
gland is seen to consist of two parts, cortical and medullary. The
cortical substance is composed of bundles of cells, separated by a
stroma, which have a different appearance in different parts. Most
superficially is the zona glomerulosa, then the zona fascicularis, and
most deeply the zona reticularis. These names convey a fair idea of the
appearance of the bundles. To the naked eye the cortical part is yellow
while the medullary is red. The medullary part consists of small islets
of cells, which resemble columnar epithelium lying among venous sinuses;
these cells are said to be in close connexion with the sympathetic nerve
filaments from the great solar plexus.
[Illustration: FIG. 3.--A, Anterior surface of right suprarenal capsule.
B, Anterior surface of left suprarenal capsule. The upper and inner
parts of each kidney are indicated in outline. On the right capsule the
dotted line indicates the upper limit of the peritoneal covering.