ORGANS OF THE BODY. 539 



which cover also, peripherally, the whole internal surface of the follicle as 

 an epithelial lining. 



Finally, the ovarium (fig. 529) generally contains a limited number of 

 mature follicles, varying from 12 to 20, which, from the fact of their 

 having been discovered at the end of the seventeenth century by an ana- 

 tomist of the name of De Graaf, have received the name of the Graafian 

 follicles. These vary in diameter, according to the maturity and size of 

 the animal, from 1 to 8 mm. (b, c). 



Fig. 532 represents such a follicle with its wall (d, e), its epithelial 

 lining (c), the ovum (a) embedded in the thick epithelial mass (b), and 

 enlarged cavity. 



In the walls of the follicle, or, as it has been named, the tJieca or mem- 

 branafollicuJi, two Iamina3 may be distinguished, an internal and external. 

 Within the first of these the ramifications of the capillaries take place, 

 while the external contains the branches (e) of the larger vessels. The 

 outer layer is composed of the same elements as the remaining sustenta- 

 cular matter of the organ, namely, of fibres of connective-tissue and very 

 densely crowded fusiform cells. 



Owing to the fact that the blood and lymphatic vessels of the tissue 

 form around the'external layer of the membrana folliculi a series of open 

 sinuous cavities, the follicle may be separated with ease, and in a perfectly 

 uninjured condition, from its surroundings. In the internal lamina of 

 the wall we then observe that the capillaries enter the latter in lines con- 



Fig. 532. Marure follicle, a, ovum ; 6, layer of epithelium enveloping the latter and lining 

 the cavity of the follicle c; rf, fibrous wall; e, external surface of the follicle. 



verging towards the centre of the follicle, forming internally a very dense 

 network with circular meshes. Like embryonic tissue this layer is parti- 

 cularly rich in cells of different forms and dimensions. Besides smaller 

 ones resembling lymphoid elements, we find another kind of larger cells, 

 roundish or poly'gonal in figure, and measuring about O0226 mm. in 

 diameter. These are, in part, situated in the intervals between the vessels, 



