STRUCTURE OF THE OVUM. 



777 



centimetres) long in front, and 3J to 4 inches (9 to 10 centimetres) long pos- 

 teriorly (Sappey). At the constricted portion of the outer opening, there is 

 a muscle, called the sphincter vaginae, and the tube is somewhat narrowed 

 at its upper end, where it embraces the cervix uteri. The inner surface pre- 

 sents a mucous membrane, marked by transverse rugae, with papillae and 

 mucous glands. Its surface is covered with flattened epithelium. The vagina 

 is quite extensible, as it must be during parturition, to allow the passage of 

 the child. It pre- 

 sents a proper coat 

 of dense, fibrous tis- 

 sue, with longitud- 

 inal and circular 

 muscular fibres of 

 the non-striated va- 

 riety. Surrounding 

 it, is a rather loose, 

 so-called erectile tis- 

 sue, which is most 

 prominent at its 

 lower portion. 



The parts com- 

 posing the external 

 organs are abund- 

 antly supplied with 



vpccpk nnrl nprvp 

 - ry es. 



In thp pli+nri wViinVi 

 lb ' WJ 



corresponds to the 

 penis of the male, and on either side of the vestibule, there is a true erec- 

 tile tissue. 



Structure of the Ovum. The description which is to follow is based 

 upon recent and extended researches into the minute anatomy of the 

 healthy human ovum (Nagel, 1888), which have been rendered possible by 

 the frequency with which, within the past few years, normal ovaries are 

 removed in surgical operations : 



The ovum lies in the Graafian follicle, embedded in the mass of granu- 

 lar cells which form the discus proligerus. Surrounding the ovum are cells 

 similar to those found in other parts of the membrana granulosa, and two 

 or three layers of columnar cells, the latter lying next the zona pellucida. 

 These columnar cells constitute the corona radiata (Bischoff). The ovum 

 itself presents the following structures : (1) Zona pellucida ; (2) peri- 

 vitelline space ; (3) a clear, outer zone of the vitellus ; (4) protoplasmic 

 zone (formative yelk) ; (5) deutoplasmic zone (nutritive yelk) ; (6) ger- 

 minal vesicle (Purkinje) ; germinal spot (Wagner). The extremely thin 

 membrane within the zona pellucida and immediately surrounding the 

 vitellus, described under the name of vitelline membrane by some anato- 

 mists, was not observed by Nagel in the human ovum. 



FIG. 283. External erectile organs of the female CLiegeois). 

 A, pubis ; B, B, ischium ; C, clitoris ; D, gland of the clitoris ; E, bulb ; F, 

 constrictor muscle of the vulva ; G, left pillar of the clitoris ; H, dorsal 

 vein of the clitoris ; I, intermediary plexus ; J, vein of communication 

 with the obturator vein ; K, obturator vein ; M, labia minora. 



