MALE REPRODUCTIVE ORGANS. 51 



Clean carefully the ventral wall of the thin cloaca, back 

 to its external aperture ; meeting on it in the median 

 line will be found a pair of thin, rounded muscles, re- 

 tractors of the penis, which pass at first backward, and 

 then, turning around another muscle, forward and dor- 

 sally to their origin. Through the ventral wall of the 

 cloaca the large, dark-colored penis will be seen. , 



122. Pass a pair of forceps through the opening of 

 the extremely distensible cloaca, and dilate the latter 

 by spreading the prongs of the forceps apart. Note 

 the penis attached for some way along the ventral side 

 of the cloaca, terminating posteriorly in a free enlarge- 

 ment (glans)^ and having a deep groove along its dorsal 

 surface. 



123. Slit the cloaca open along one side, taking care 

 not to injure the penis, and examine the latter ; it is 

 composed of two elongated corpora cavernosa placed 

 side by side, and in contact in the median line. Each 

 corpus cavernosum, narrowing as it runs forward, ends 

 anteriorly in a highly vascular dilatation or bulb. This 

 is best seen through the ventral side of the cloaca. 



124. Make a small hole in a vein which leaves the 

 bulb upon its ventral and outer side ; insert the end of 

 a blow-pipe and inflate the penis ; note its extreme dis- 

 tensibility, and how it becomes erect when distended. 

 The corpora cavernosa at the same time swell up and 

 press against each other, converting the groove on the 

 dorsum of the penis into a canal. Observe, also, the 

 great distention of the glans, and the elevated lips bound- 

 .ing the end of the urethral groove on it ; also, the cur- 



