Anatomical study of the infra-montanal urethra in man.

Five samples infra-montanal prostatic urethra fixed in formalin and stored in liquid nitrogen at -30C were examined histologically. The results of this study demonstrated that muscle fibres of the striated sphincter extend as far as the level of the verumontanum. The proportion of rapid and slow striated fibres was identical. These striated fibres were mixed with smooth muscle fibres of the urethra. The density of innervation of this muscular tunic was found to increase closer to the striated sphincter; it is composed of equal numbers of adrenergic and cholinergic fibres.