684 



THE REPRODUCTIVE ORGANS 



blood-vessels and nerves enter it. Each ovary is about 4 cm. long, 2 cm. wide, 

 and 1.25 cm. thick. It is supported by the suspensory ligament. 



The internal structure of the ovary consists of a peculiar soft fibrous con- 

 nective tissue, stroma, abundantly supplied with blood-vessels. The surface 

 of the ovary is covered with cubical epithelium. Embedded in the stroma in 

 various stages of development are numerous minute follicles cr vesicles, the 

 Graafian follicles, containing the ova, figure 494. They are small and numer- 

 ous near the surface of the ovary, either arranged as a continuous layer, as 

 in the cat or rabbit, or in groups, as in the human ovary. Nearer the center 

 are large and fully developed follicles. 



Each follicle has an external membranous envelope, or membrana propria, 

 which is lined with a layer of nucleated cells, forming a kind of epithelium 



FIG. 493 . Diagrammatic Section of the Ovary, Showing its Cortical or Ovigenous Layer, Formed 

 of Ovisacs in Various Stages of Evolution. (Duval.) A, A, A, Primordial ovisacs; B, B, B, ovisacs 

 further developed; C, ovisac approaching maturity; D, ripe ovisac with its proligerous disc (DP) 

 containing the ovum; MG, membrana granulosa; H, hilum of ovary. 



or internal tunic, and named the membrana granulosa. The cavity of the 

 follicle contains the ovum enclosed in a very delicate membrane. The large 

 spherical nucleus contains one or more nucleoli. The nucleus is known as 

 the germinal vesicle, and the nucleolus as the germinal spot. 



The human ovum measures about 0.2 mm. in diameter. Its external 

 investment, or the zona pellucida, or vitelline membrane, is a transparent 

 membrane, about 10 ^ in thickness, which under the microscope appears 

 as a bright ring, figure 495. The ovum itself has the characteristic structure 

 of the typical cell, with the exception that its cytoplasm is filled with numerous 

 yolk granules. The larger granules cr globules, which have the aspect of 

 fat-globules, are in greatest number at the periphery of the yolk. 



The nucleus, or germinal vesicle, is about 0.05 mm. in diameter. The 

 vesicle is of greatest relative size in the smallest ova. 



The Graafian follicles are formed in the following manner: The em- 



