86 ANATOMY OF THE KAT 



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 longi- 

 tudinal groove on its ventral surface marks the position 

 of the septu^m 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 num- 

 ber of layers in it. A muscular sac will be observed im- 

 mediately 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 



