578 ABDOMEN 



This is the longest division of the urethra. It is embedded 

 in the substance of the corpus cavernosum urethras, and its 

 calibre varies considerably at different points. In each 

 expansion of the corpus cavernosum urethras, viz. the bulb 

 posteriorly and the glans anteriorly, .there is a corresponding 

 dilatation of the urethra ; between the dilatations the canal 

 is of uniform diameter, and slightly wider than the membranous 

 portion. The dilatation of the urethra in the glans is termed 

 the fossa navicularis. At its orifice, the external urethral 

 orifice (meatus urinarius), the canal is much contracted, and 

 is even narrower than any part of the membranous portion. 

 The orifice is a vertical slit, and its lower end is connected 

 with the prepuce by a fold of skin, termed thefrenu/um preputii. 



In the bulb and in the glans penis the erectile tissue of 

 the corpus cavernosum urethroe is disposed very unequally 

 around the urethra. In the former it is chiefly massed below 

 or behind the tube, whilst in the glans it is chiefly placed in 

 front and on each side, a very thin layer lying posteriorly. 



The ducts of the bulbo-urethral glands (Cowper's) pierce 

 the floor and open into the cavernous part of the urethra about 

 an inch in front of the inferior fascia of the uro-genital 

 diaphragm. The orifices are extremely minute and difficult 

 to find, but by making a small hole in the wall of the duct, 

 as it emerges from the gland, and passing a fine bristle along 

 it, the dissector may be able to find the opening in the 

 urethral floor. After piercing the uro-genital diaphragm the 

 ducts proceed forwards, first in the erectile tissue, and then 

 in the submucous layer, towards their terminations. 



The walls of the urethra are always in apposition except 

 when urine is flowing through it, and a transverse section 

 through the spongy portion, except at its anterior part, has the 

 appearance of a transverse slit. In the fossa navicularis, how- 

 ever, the slit becomes vertical, showing that there the side 

 walls are in contact. 



Mucous Membrane of the Urethra. The mucous lining 

 of the urethra is continuous posteriorly with that of the 

 bladder, and anteriorly with the integument of the glans 

 penis. It is continuous also with the mucous membrane of the 

 various ducts which open into the urethra. Scattered over 

 its whole surface are the mouths of numerous minute recesses, 

 laucncz urethrales. As a general rule, their openings are 

 directed forwards, and they are largest on the dorsal wall, 



