268 THE VISCERA. 
each is covered by a muscle (ischiocavernosus). The clitoris 
is said to contain a bone. 
Mammary Glands.—The mammary glands secrete the 
milk, and lie on the ventral surface of the body beneath the 
integument. The separate glands are closely gathered into 
two chief masses, one on each side the ventral middle line. 
Each of these extends from about the region of the fourth rib 
to the caudal end of the abdomen, ending over the pubic 
symphysis. On each side the glands are gathered into five 
groups, each of which is furnished with a nipple. The nipple 
is a projection of the integument, having near its distal end 
numerous fine openings for the ducts of the glands. The first 
two nipples are on the thorax, the other three on the abdomen, 
the most caudal ones being about two or three centimeters in 
front of the cranial edge of the pubis. 
Rudimentary mammary glands and nipples are present in 
the male. 
MUSCLES OF THE UROGENITAL ORGANS, RECTUM, AND 
ANUS (Figs. 113 and 114).—The muscles connected with the 
caudal openings of the alimentary canal and of the urogenital 
organs are closely interrelated, a single muscle sometimes 
acting on parts of both systems. For this reason all these 
muscles are described together. 
The region lying between the anus and the external open- 
ing of the urogenital organs is known as the perineum. The 
perineum is formed chiefly by muscles and fascia. 
a. Muscles common to the Male aud Female.—M. sphincter 
ani externus (Fig. 113, 7; Fig. 114, @).—This muscle is con- 
founded with the levator scroti (Fig. 113, 7) or the levator 
vulve (Fig. 114, 4). The two take origin in common from the 
integument on the dorsum of the root of the tail dorsad of the 
fifth caudal vertebra. There the fibres from the opposite sides 
are intermingled. The common muscle passes ventrad about 
the tail as a flat band close to the integument. Dorsad of the 
anus the inner fibres of the muscles of the opposite sides are 
united. They then separate and surround the anus as a band 
five millimeters wide situated beneath the integument. Ven- 
trad of the anus the fibres are again intermingled. Some fibres 
