External Perineum

The development of the characteristic external shape of the perineum mirrors the strong proliferation of stromal elements during the first half of this postcloacal sexually indifferent period (Figs. 1, 10). The combined rapid growth of fibrovascular tissues embracing the urogenital sinus ventrally and the more (myo)fibroblastic tissues embracing the sinus dorsally create a cylindrical phallic structure, with the future erectile elements forming most of its protruding parts and the future...

Vagina

Investigations into the development of the vagina have led to a profusion of different and often controversial theories (O'Rahilly 1977). These ideas will be addressed in the context of the present observations arranged in the sequence of developmental events. The present observations confirm the earliest events, i.e., the formation of the paramesonephric ducts, as have been described by Gruenwald (1941) and Frutiger (1969). The present study reveals, however, that the distal tips of the...

Anal Canal

The anal canal forms a narrow tube lined by ps.str.col. epithelium. Initially it does not reveal features which discriminate it from the gut cranially (Fig. 16a). However, before long a subtle difference appears between the mucosa of that most distal part of the gut, i.e., rectum, and that of the cloaca-derived portion, which then shows a less regular distribution of nuclei in the epithelium and a more longitudinal orientation in the texture of the lamina propria and forms the cloaca-derived...

Vestibulum

The descent of the caudal vagina and its orifice not only combines the dorsal wall of the original deep urogenital sinus caudal to the orifice with the whole of the superficial urogenital sinus in the formation of the vestibulum, but also influences an alteration in its shape from an irregular trumpet-like duct into a wider and more shallow chamber (Figs. 18, 21). Additional factors determining its shape are a deepening of the dorsal groove and the adjacent parts of the cranially converging...

Penis Prepuce Preputial Sac and Frenulum

Preputial Sac

Basic to the formation of the penis is the combined growth of the fibrovas-cular glans, corpora cavernosa, and corpus spongiosum embracing the early urethra ventrally, and of the stromal tissues that embrace the early urethra dorsally and are situated in the base of the early penis. The growth of the dorsal stromal elements not only makes the urethral orifice shift distalward but also envelops the lengthening urethra and ventral erectile structures in a number of fascial layers. This combined...

Introduction On Perineum

Descriptions of the development of the sexually indifferent perineum tell how the widened caudal part of the hindgut becomes the cloaca after being contacted by the mesonephric ducts. This cloaca is thereafter divided into a urogenital part into which issue the allantois and mesonephric ducts and an anal part which receives the gut. Traditionally almost all attention of embry-ologists has been focused on this process of partition, most likely because disturbances in this process have been...

Perineal Raphe Septum Body and Fasciae

No information was available from the literature about the differentiation of stromal tissues of the penis complementary to the erectile structures. The present study demonstrates the special orientation of the fibers and their arrangement into the perineal raphe and septum and into the various fasciae. The analysis presented here demonstrates that the perineal raphe, perineal septum and body, and fasciae form a composite histological structure based on the diversity in tissues involved in its...

Observations

The first signs of the development of a male type of perineum are identified at the very start of the fetal period. The sexually indifferent perineum at that stage reveals a marked preponderance of urogenital structures derived from the ventral part of the cloaca over anal elements derived from its dorsal part. Where both structures meet, a small midperineal region is formed. It is the transformation of that urogenital part which will give the perineum its conspicuous male composition, major...

Urogenital Sinus

The term urogenital sinus has been applied to different structures. Originally it was used to indicate that portion of the ventral cloaca situated between the orifices of the mesonephric ducts and the cloacal membrane, later (after disintegration of this membrane) urogenital orifice. The short cranial segment of the cloaca between the mesonephric orifices and the bladder was named urethra (Mijsberg 1924), primary urethra (Chwalla 1927), or primitive urethra (Hamilton and Mossman 1972), thus...

Transformation of the Urogenital Sinus into the Urethra and Vestibulum

Vestibulum Vaginae

The descent of the caudal part of the vagina and its orifice (f.60 -110 mm) has as a major consequence that parts of the wall of the original urogenital Fig. 21a-c Schematic median sections through female fetuses of 40 mm to 125 mm to demonstrate the rearrangement of segments of the wall of the urogenital sinus during its transformation into the urethra and vestibulum in association with the descent of the vagina. These demonstrate how the urethra is composed by the combination of the whole of...

Urethra

The present observations on the development of the deep urethra, i.e., pros-tatic and membranous urethra differ from earlier data only in detail. They are in conformity with information on its developing shape (Johnson 1920 Chwalla 1927) and the formation of the prostate (Herzog 1904 Lowsley 1912 Chwalla 1927). Confirming the opinion of Herzog (1904), it is established that its epithelium is pseudostratified columnar and not transitional as is still generally believed. This is a characteristic...