iv THE GENEKATIVE SYSTEM OF THE MALE 147 



For the propulsion of the seminal fluid along the urethra to 

 the ineatus, from which it spirts out in successive jets, rapidly 

 following one another wit Ir irregular rhythm, there enter into 

 play other expulsive forces, developed by the smooth and striated 

 muscles with which the prostatic and membranous parts of the 

 urethra are provided. The smooth muscle is disposed in two 

 strata an internal longitudinal, which may be considered as the 

 continuation of the muscular tunic of the bladder, and the 

 muscular portion of the corpus 

 spongiosuin of the urethra, and 

 an external circular layer which 

 anatomists call the internal 

 sphincter of the bladder. The 

 striated muscle is in fibres dis- 

 posed circularly, and constitutes 

 the sphincter of the prostatic 

 and membranous parts of the 

 urethra of Henle, forms the 

 essential part of the muscle of 

 the urogenital trigone, is pro- 

 longed distally towards the 

 beginning of the corpora caver- 

 nosa of the penis, and continues 

 straight on with the deep part 

 of the bulbo-cavernosus muscle 

 (Figs. 39 and 27). 



The smooth muscle of the 

 urethra, the contraction of which 

 is involuntary in type, causes 

 the closure of the internal open- 

 ing of the urethral canal, which 

 renders difficult the emptying 

 of the bladder in semi-erection 

 of the penis, and prevents it 

 altogether when erection is 

 complete. During the reflex 

 ejaculatory act it contributes 

 to the expulsion of the semen along the urethra, and prevents 

 it ascending in a retrograde direction towards the neck of the 

 bladder. Walker (1899) is of opinion that the contraction 

 of the internal longitudinal portion of this muscle produces a 

 dilatation and shortening of the membranous urethra, and thus 

 facilitates by aspiration the escape of the spermatic and prostatic 

 secretions ; whilst the contraction of the external circular portion, 

 which follows at intervals, prevents the reflux of the seminal fluid 

 into the bladder and impels it towards the external meatus of the 

 urethra. If it could be shown that the two parts of the muscle 



VOL. v L 2 



FIG. 30. Diagram showing in sagittal section 

 the muscular apparatus of the urethra. The 

 smooth muscles are indicated in blue and the 

 striated in red. (Chiarugi.) F, bladder ; P, P, 

 prostate ; B, bulb of urethra ; 1, prostatic 

 urethra ; II, trigonal membranous urethra 

 ///, pre-trigonal urethra ; IV, urethra caver- 

 nosa ; me, thickening of median stratum of 

 muscles of bladder, corresponding to anterior 

 outline of internal orifice of urethra ; siv, 

 posterior segment of the internal sphincter 

 of the bladder in continuation of the muscu- 

 lature of the trigonum vesicale ; sirf, anterior 

 segment of internal sphincter muscle of 

 bladder ; c, external circular stratum of smooth 

 muscle of urethra ; Z, internal longitudinal 

 stratum of same ; ss, ss, trigonal and bulbo- 

 urethral part of striated sphincter of urethra ; 

 ss', prostatic portion of same. 



