THE URETHRA 207 



no niiiscularis luiicosa, the suhiiiucosa of fihroclastic connective 

 tissue unites with the tunica ])ro])ria undcrlx in<,^ the epithelial lining. 

 A study of a cross-section of relaxed hladder wall shows a thick 

 muscularis. The nniscnlaris coat is divided into a thick middle 

 coat with circularly arranged cells, an innermost region with a thin 

 layer of longitudinally arranged cells, and an outside region also 

 with longitudinal layers of cells. The muscle tissue, although 

 loosely arranged, is very strong. The fibrosa consists of fibroelastic 

 connective tissue and merges with a ])erit()neal-like coating. At 

 the junction of the hladder with the urethra there is a ring of cir- 

 cularly disposed smooth nuiscle, the internal sphincter of the bladder. 



THE URETHRA. 



The urethra differs in the male and fenuile. In the male it forms 

 the duct of the penis, and an account of its structure will l)e con- 

 sidered with the male system of reproduction. The female urethra 

 is short. (Fig. lol.) It extends from the bladder to the vestibule 

 and opens into the vestibule along with the vaginal part of the female 

 reproductive system. Internally it presents longitudinal folding of 

 the mucosa. The epithelium of the mucosa is conunonly of the 

 stratified squamous variety. There is no distinct subnuicosa; out- 

 side the tunica ])ropria is a muscularis coat with an inner longi- 

 tudinal coat and an outer circular coat. Outside the nniscnlaris is 

 a fibrosa. Near the junction of the ureter with the ^•estibule there 

 is a sphincter nniscle of the skeletal \'ariety outride the smooth 

 muscle. 



REFERENCES. 



Chase, S. W. 1923. The mesonephros and urogenital ducts of Necturus 



maculosus (Rufinesque), Jour. Morph., 37, 457. 

 Defrise, a. 1932. Cytophysiological studies of the nephrocytes of uni- 



segmental aglomerular and glomerular nej^hrons, Anat. Rec, 54, 185. 

 Edwards, J. G. 1928. Studies on aglomerulai- and glomeiular kidneys. Am. 



Jour. Anat., 42, 75. 

 1933. The renal unit in the kidney of vertebrates. Am. Jour. Anat., 



53, 55. 

 Gersh, I. 1934. Histochemical studies on the mammalian kidney: II. The 



glomerular elimination of uric acid in the rabbit, Anat. Rec, 58, 369. 

 Grafflin, a. L., and Moses, J. E. 1934. A microfluoroscopic study of tele- 



ostean kidneys, Anat. Rec, 59, 449. 

 Gray, P. 1930. The development of the Amphibian kidney: Part I. The 



development of the mesonephros of Rana temporaria, Quart. Jour. Micr. 



Sci., 73, 508. 



