Towards a rational terminology in the study of the gubernaculum testis: arguments in support of the notion that the cremasteric sac should be considered the gubernaculum in postnatal rats and other mammals.

There is need for a consistent definition of structures caudal to the testis that variously are termed 'gubernaculum testis' as a basis for understanding the emergence and sexually dimorphic further growth and differentiation of this specifically mammalian structure. Rodent fetuses undergo a stage of development during which there is almost complete unanimity as to the definition of the 'gubernaculum' as a papilla-like structure (often called conus inguinalis) protruding from the area of the internal inguinal ring. This structure shows at least 3 readily distinguishable components before birth. Postnatally, the papilla-like gubernaculum starts to undergo inversion to become the tunica of the sac-like processus vaginalis. The 3 components of the fetal gubernaculum develop further uninterruptedly, but with a different spatial arrangement, as parts of the wall of a sac rather than as parts of a papilla-like structure. Comparison of this process in rodents with that in other mammals (pig, horse, man) revealed an essentially identical emergence of a papilla-shaped gubernaculum with similar constituents. Initial development of the processus vaginalis also began with the inversion of the gubernacular papilla. Cattle fetuses appeared exceptional as outgrowth of the processus vaginalis occurred without a preceding papilla-shaped gubernaculum in the area of the inner inguinal ring. The findings lead to the following conclusions. (1) In rodents, the whole of the postnatally developing processus vaginalis, including therefore its cremasteric muscles but without the attached genital mesentery, is to be viewed as the male postnatal gubernaculum. Sexual differentiation of the gubernacular primordia includes a sex-specific effect on the morphogenesis of all constituents of the processus vaginalis sac including cremasteric muscle cells. (2) Gubernacular growth and differentiation appear essentially a uniform process throughout the placentalia mammalian class; only quantitative differences occur in the extent of initial development of an intra-abdominal conus inguinalis and later cremaster muscles.