DEVELOPMENT OF TESTES AND OVARIA. 949 



the terminations of the urethra and of the Wolffiian ducts, and which re- 

 mains permanently unclosed. In the Male, on the other hand, the sinus 

 ycnitali* makes no advance in development, and diminishes in relative si/c; 

 so at the period of foetal maturity, it is only discoverable as the ve^icn/a 

 prostatica, which has been supposed until recently to be an appendage to the 

 prostate gland. A transverse constriction in this canal marks out its vaginal 

 from its uterine portion ; the former having exactly the same relation as in 

 the female to the terminations of the urethra and of the Wolrfian ducts 

 (vasa defereutia) in the " urogenital sinus," which is subsequently closed in, 

 however, so as apparently to form a continuation of the urethral canal; and 

 the latter, in those Mammals whose females have a " uterus bicornis," ex- 

 hibiting a like divarication into two lateral halves. 1 



789. The history of the development of the external Organs of Generation 

 in the two sexes, presents matter of great interest, from the light which is 

 thrown by a knowledge of it upon the malformations of these organs, which 

 are among the most common of all departures from the normal type of Hu- 

 man organization. Not only is the distinction of sexes altogether wanting 

 at first; but the conformation of the external parts of the apparatus is origi- 

 nally the same in Man and the higher Mammalia as it permanently is in 

 the Oviparous Veriebrata. For, about the 5th or 6th week of embryonic 

 life, the opening of a cloaca may be seen externally, which receives the ter- 

 mination of the intestinal canal, the ureters, and the efferent ducts of the 

 sexual organs; but at the 10th or llth week, the anal aperture is separated 

 from that of the genito-urinary canal or "uro-genital sinus," by the develop- 

 ment of a transverse band; and the uro-genital sinus itself is gradually sepa- 

 rated by a like process of division, into a "pars urinaria" and a "pars geni- 

 talis," the former of which, extending towards the urachus, is converted into 

 the urinary bladder. A partial representation of this phase of develop- 

 ment is found in the permanent condition of the Struthious Birds and of the 

 Implacental Mammalia. The external opening of this canal is soon observed 

 to be bounded by two folds of skin, the rudiments of the labia majora in the 

 female, and of the two halves of the scrotum in the male; whilst between 

 and in front of these, there is formed an erectile body, surmounted by a 

 gland, and cleft or furrowed along its under surface. This body in the female 

 is retracted into the genito-urinary canal, and becomes the clitoris, whilst 

 the margins of its furrow are converted into the nymphse or labia minora;. 

 and these bound the "atrium vaginre" or "vestibule," which receives the 

 orifices of the urethra, of the vagina, and of Gaertner's canals when they are 

 present, and which exactly represents, therefore, the "sinus genitalis" of the 

 early embryo. In the male, on the other hand, this sinus is nearly closed 

 in at a very early period, by the adhesion of the two folds of integument 

 which bound it, forming that portion of the genito-urinary canal (improperly, 

 termed the " urethra") which receives the orifices of the vesical or true urethra, 

 of the genital sinus (vesicula prostatica), and of the vasa deferentia; the erec- 

 tile body increases in prominence, and becomes the penis; whilst the margins 

 of the furrow at its under surface unite (at about the 14th week), to form 

 the anterior continuation of the now contracted geuito-uriuary canal, which 

 is commonly termed the spongy portion of the urethra. The following table, 



1 See Prof. E. Weber's Zusatze zur Lohre vom Bane und den Verrichtun^en der 

 Geschlechtsoryane, Leipzig, 1846; and Dr. Leuckart's Art. Vesictila Prostatica, in 

 Cyclop, of Anat. and Physiol., vol. iv It was supposed by Prof. Weber that the 

 vesicula protatica is the homologue of the uterus alone; but the Author consider it 

 to have been satisfactorily established by the researches of Dr. Leuckart, that -it an- 

 swers to th*e uterus and vagina conjointly. 



