muscle. Rats dissected in the laboratory frequently show the testes more or less completely retracted into the abdomen.
The scrotum of the rat is a prominent swelling, about four centimeters long in a large male, lying on the ventral side of the body between the anus and penis. Like the rest of the integument it is covered with hair. A longitudinal groove on its ventral surface marks the position of the septum scroti, an internal partition which separates one testis from the other.
Carefully slit the scrotum ventrolaterally on one side throughout its entire length, using care to cut no deeper than the integument. Cautiously separate the integument, which is the scrotum proper, from the underlying layer of connective tissue. This connective tissue forms a sac which joins a similar sac surrounding the other testis to form a median partition, the septum scroti. Slit the connective tissue sac lengthwise and determine the number of layers in it. A muscular sac will be observed immediately under the connective tissue. It may be traced forward to the ventral abdominal muscles. Microscopic examination of a piece of this muscle will show that it is two-layered and that the fibers are cross striated. The fibers of one layer cross those of the other nearly at right angles.
Each testis is an ovoid body about two centimeters long. It lies lengthwise of the scrotum. The epididymis is closely associated with the testis phylogenetically, structurally, and functionally. It comprises three parts. The enlarged anterior end, or caput epididymidis (head), curves around the anterior end of the testis, and is attached ventrally and mesially to it by a mesentery. The slender corpus epididymidis (body) passes along the dorsal side of the testis, connecting the caput epididymidis in front with the
