546 MANUAL OF HISTOLOGY. 



If we examine a recently ruptured follicle very minutely, we notice in 

 many instances the internal tunic projecting into the cavity on either 

 side in folds (fig. 538, d*). These folds consist of young exuberant cell- 

 growths, and contain in their 

 axes fasciculi of hard ill-de- 

 veloped fibrous tissue. On 

 the coming in contact of the 

 apices of the folds a peculiar 

 system of septa is formed of 

 the latter, the cells constituting 

 the yellow substance of the 

 corpus luteum. 



If, again, a completed corpus 

 luteum (of a cow, for instance, 

 His) be closely examined, it is 

 found to have a peculiar radi- 

 ating structure, produced by 



Fi 6:jg filamentous bands passing out 



from a central fibrous nucleus, 



the so-formed interspaces being occupied by a soft yellow substance. 

 The whole is enclosed within the external membrane of the follicle to 

 which the septa are attached. The vascularity of the corpus luteum is 

 extremely great, and it contains, like the rest of the ovary, numerous 

 lymphatic vessels. In fact, this yellow mass may be numbered among 

 the most vascular parts of the whole body, so highly developed is its capil- 

 lary network. 



Beside this vascular framework we find two forms of cells in the yellow 

 substance. In the first place, there are fusiform elements, 0'0338-0'0451 

 in length and O'OOSG-O'OOGS mm. in breadth, with oval elongated nuclei ; 

 and then, again, we meet with larger cells. 0'0226-0'0451 mrn. in diameter, 

 of various shapes, and containing yellow fatty granules within them 

 (iig. 95, a, p. 95). The former invest at all points the highly deve- 

 loped vascular network of the part like the cells of a rudimentary 

 adventitia. The latter, on the other hand, occupy the narrow meshes 

 between these. Thus the general structure of the mature corpus luteum 

 corresponds with that of the membrana internet, of a fully developed 

 Graqfian vesicle. 



The yellow body, however, does not long remain in this condition of 

 exuberant growth. It soon begins to undergo a process of retrograde 

 development, diminishing at the same time in magnitude (fig. 538, e). 

 This change commences in all probability in a decay of the afferent 

 arterial tubes, which are now found to possess enormously thickened 

 walls (His). For some time we may still recognise, besides the vanishing 

 yellow mass, the remains of the fibrous septal system, and external follicle 

 membrane, distinguished by its dark brown pigments contained in cells. 

 This colouring matter is laid down along the course of the vessels, and is 

 possibly metamorphosed haemoglobin. 



As soon as this pigment has been absorbed, the yellow substance, 

 formerly so abundant, melts gradually away with the adjacent ovarian 

 tissue, until it is no longer recognisable. 



The time consumed in this retrogressive process varies considerably. 

 When pregnancy does not supervene upon menstruation, the changes 

 mentioned follow one another in rapid succession. But if gravidity takes 



