The =prepuce= (Præputium), popularly called the “sheath,” is a double
invagination of the skin which contains and covers the free or
prescrotal portion of the penis when not erect. It consists of two
parts, external and internal. The external part or sheath extends from
the scrotum forward close to the umbilicus, where the external layer is
reflected ventrally and laterally, forming the thick margin of the
=preputial orifice= (Ostium præputiale); dorsally it is directly
continuous with the integument of the abdominal wall. It is marked by a
median =raphé præputii=, a continuation of the scrotal raphé. At the
lower margin of the preputial orifice there are often in the stallion
two papillæ, which are rudimentary teats or nipples. The internal layer
=passes= backward from the preputial orifice a distance of about six to
eight inches (ca. 15 to 20 cm.), lining the cavity of the external
prepuce, and is then reflected forward until it approaches the orifice,
where it is again reflected backward. It thus forms within the cavity of
the sheath a secondary tubular invagination, the prepuce proper, in
which the anterior part of the penis lies. This tubular cavity is closed
behind by the reflection of the internal layer on to the penis to form
the penile layer of the prepuce. Its orifice is surrounded by a thick
margin, the =preputial ring= (Annulus præputialis), which is connected
ventrally with the outer part of the sheath by the =preputial frenum=
(Frenulum præputii).
The arrangement differs from that found in man in the fact that the
inner part of the prepuce as described above is equivalent to the
entire human prepuce. This part, the prepuce proper, is well seen on
sagittal sections, and can be demonstrated by pulling the penis,
inclosed in this prepuce, out of the cavity of the sheath; the
arrangement of the free part of the penis and prepuce is then like
that in man. (In paraphimosis the penis is strangulated by the
preputial ring.)
[Illustration: