ANATOMY OF THE .MALE ORGANS OF GENERATION 71 



sebaceous glands which exist in and beneath it. It is this substance which, 

 on becoming inspissated and dry, forms the dark gray masses which 

 accumulate in the scrotum, and sometimes provoke irritation and disease. 

 During erection this inner layer is effaced, and forms a covering to the body 

 of the organ as it protrudes from the prepuce. The sheath is supported by 

 an elastic band — "suspensory ligament" of the sheath — reflected from the 

 under surface of the abdomen. 



The loud gurgling sound emitted by some horses when in motion is 

 due to the sudden displacement of air by the to-and-fro movements of the 

 penis within the sheath. 



URETHRA 



The urethra (d and K, fig. 226) is a long tube extending from the 

 bladder to the end of the penis. It conducts the urine out of the body, 

 and serves also to convey the spermatic fluid and some other secretions 

 accessory to reproduction into the female organs of generation in the act 

 of copulation. 



In proceeding from the neck of the bladder, the urethra passes back- 

 wards for a short distance along the floor of the pelvis; then curving down- 

 ward over the ischiatic arch, it takes a direction forward between the two 

 branches or cruree of the corpora cavernosa, from which it continues onward, 

 enclosed in the corpus spongiosum, to the glans penis. There it ends in a 

 small cylindrical projection termed the "urethral tube". On leaving the 

 neck of the bladder it is surrounded by the prostate gland, and then for a 

 farther short distance by a thin muscle, the " compressor urethrae ", after 

 which it is enclosed in the corpus spongiosum for the remainder of its 

 course, excepting the small terminal prolongation from the glans penis. 



These three divisions are distinguished as (l) the "prostatic", (2) the 

 "muscular" or "membranous", and (3) the "spongy" portion. An 

 inspection of the interior of the canal shows it to vary in diameter in 

 different parts of its length. The smallest part is the external opening, 

 which will admit a catheter about half an inch in diameter. It may be 

 concluded, therefore, that any instrument that will enter this opening may 

 be safely pressed on into the bladder. The larger parts are the prostatic, 

 and those situated at either extremity of the spongy portion. 



Openings into the Urethra. — Besides the inlet from the bladder by 

 which the urine escapes, there are a number of openings into the urethral 

 canal. In the prostatic portion, on either side of a small ridge of mucous 

 membrane, is the orifice of the " ejaculatory duct", through which the 

 seminal fluid is discharged in the act of copulation. These openings in 

 aged stallions are of considerable size, in some instances sufficiently large 



