HISTOLOGY 149 



tinue their course in the medulla which contains many large blood vessels 

 separated from each other by a rather dense fibrous stroma. The free 

 surface of the cortex is covered by a layer of cuboidal epithelial cells, the 

 germinal epithelium, beneath which a thin layer of dense fibrous connective 

 tissue forms the tunica albuginea. The primary folUcles are immediately 

 beneath the tunica albuginea, while those which are further developed are 

 more deeply located. 



A primary follicle consists of a large spherical cell, the primary oocyte, 

 surrounded by a layer of squamous follicular cells. The nucleus of the 

 oocyte is vesicular, contains small chromatin granules and a prominent 

 nucleolus. Follicles which are somewhat further developed are lined by two 

 or more layers of cuboidal follicular cells. Each such follicle contains a 

 larger oocyte which is separated from the follicular cells by a transparent cell 

 membrane, the zona pellucida. The connective tissue cells of the stroma 

 are arranged concentrically around the follicle and form the theca folliculi. 

 Around the larger follicles this layer has an inner part, the theca interna, 

 which is rich in capillaries and contains large, loosely arranged cells, and an 

 outer part, the theca externa, which contains concentrically arranged dense 

 fibers. 



In those folHcles in which the development is still further progressed, 

 small irregular spaces filled with a clear fluid, the primary liquor folliculi, 

 appear among the follicular cells. These spaces gradually open into each 

 other and form a single large fluid-filled cavity, the antrum. The antrum is 

 lined by a stratified layer of follicular cells which in this position sometimes 

 are called granulosa cells and which form the membrana granulosa. This 

 membrane is thicker in the region where the oocyte, encircled by a group of 

 follicular cells to form the cumulus oophorus, is attached. The follicular 

 cells which immediately surround the zona pellucida are elongated and 

 radially arranged. They are attached to the ovum by delicate cytoplasmic 

 processes and form the corona radiata. The formation of the antrum and 

 the increase in the amount of the liquor foUiculi enlarges the follicle. Due to 

 this expansion the follicle extends to the surface of the ovary and finally 

 bulges out into the periovarian space. Such a follicle is called a mature 

 vesicular or Graafian follicle. According to Brambell (11) the mean 

 diameter of a ripe follicle in a section is about 530 ju. A single follicle may 

 occasionally contain two or more ova. 



Changes preceding and following ovulation.— Tht primary liquor 

 folliculi becomes more viscid as estrus approaches. Preceding ovulation 

 the secondary liquor folliculi is formed which is more fluid in character (85). 



