Text-book of the embryology of man and mammals / by Oscar Hertwig ; translated from the third German edition by Edward L. Mark.

Date:: 1892

Credit: Text-book of the embryology of man and mammals / by Oscar Hertwig ; translated from the third German edition by Edward L. Mark. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

413/704 (page 385)

$NAGEL has studied tlie development of the testis in human embryos. Accord- ing to his description also, there arise from the actively proliferating germinal epithelium numerous cords, in which large primitive seminal cells are imbedded. The cords afterwards become the seminiil tubules. In Man there prevails from tlie beginning, as Nagel remarks, such a great difference between the two sexes, both in the form of the original germinal ridge and in the whole process of its differentiation, that one can recognise in the anatomical structure of the sexual glands from a very early stage whether one has before him a male or a female. (h) Metamorphosis of the Different Fundaments of the Urogenital System into the Adult Condition. We have become acquainted in the preceding pages with the fir.«it development of the various parts which constitute the foundations of the urogenital system. These are (fig. 219) three pairs of canals —the mesonephric ducts (ug), the Miillerian ducts {nig), and the ureters (Jil)—and in addition a great number of glandular structures —pronephros, mesonephros (im), metanephros (?^), and the sexual glands (Jed), ovary and testis. It will be my task in what follows to indicate how the ultimate condition is derived from these embryonic fundaments. In this I shall limit myself, in the main, to Man, because we now have to do with more easUy investigated, and in general well-known conditions. In a human embryo eight weeks old (fig. 220) the fundaments, if we neglect differences which are recognisable only by the aid of the microscope, are so similar in male and female as to be indistinguishable. All the glands lie at the sides of the lumbar vertebrEB: farthest forward the kidney (w), which is a small bean-shaped body ^ upon this lies the suprarenal body (nn), that at this time is dispropor- tionately large and is to be seen only on the left half of the figure. Somewhat lateral to the kidney one sees the primitive kidney (un) as an elongated, narrow tract of tissue. It is attached to the wall of the trunk by a connective-tissue lamella, a fold of the peritoneum, the so-called mesentery of the primitive kidney. In the middle of the gland it is rather broad, but above, toward the diaphragm, it IS elongated into a narrow band, which Kolliker has descrilaed as the diaphragmatic ligament of the primitive Iddney. Upon careful examination one also observes at the lower end of the primitive Iddney a second fold of the peritoneum, which runs from it to the inguinal region (figs. 219 and 220 gh). It encloses a firm strand of connective tissue, a kind of ligament, that is destined to play a 25$