238 HAND-BOOK OF PHYSIOLOGY. 



zona pellucida, or vitelline membrane. Whether the germinal spot is 

 formed first, and the germinal vesicle afterward developed around it, can- 

 not be decided in the case of vertebrate animals; but the observations 

 of Kolliker and Bagge on the development of the ova of intestinal worms 

 show that in these animals, the first step in the process is the production 

 of round bodies resembling the germinal spots of ova, the germinal 

 vesicles being subsequently developed around these in the form of trans- 

 parent membranous cells. 



From the earliest infancy, and through the whole fruitful period of 

 life, there appears to be a constant formation, development, and matura- 

 tion of Graafian vesicles, with their contained ova. Until the period of 

 puberty, however, the process is comparatively inactive; for, previous to 

 this period, the ovaries are small and pale, the Graafian vesicles in them 

 are very minute, and probably never attain full development, but soon 

 shrivel and disappear, instead of bursting, as matured follicles do; the 

 contained ova are also incapable of being impregnated. But, coincident 

 with the other changes which occur in the body at the time of puberty, 

 the ovaries enlarge, and become very vascular, the formation of Graafian 

 vesicles is more abundant, the size and degree of development attained by 

 them are greater, and the ova are capable of being fecundated. 



Fallopian Tubes. The Fallopian tubes are about four inches in 

 length, and extend between the ovaries and the upper angles of the 

 uterus. At the point of attachment to the uterus, the Fallopian tube is 

 very narrow; but in its course to the ovary it increases to about a line 

 and a half in thickness; at its distal extremity, which is free and floating, 

 it bears a number 6f fimbrim, one of which, longer than the rest, is 

 attached to the ovary. The -canal by which each Fallopian tube is 

 traversed is narrow, especially at its point of entrance into the uterus, at 

 which it will scarcely admit a bristle, its other extremity is wider, and 

 opens into the cavity of the abdomen, surrounded by the zone of fimbrige. 

 Externally, the Fallopian tube is invested with peritoneum; internally, 

 its canal is lined with mucous membrane, covered with ciliated epithe- 

 lium: between the peritoneal and mucous coats, the walls are composed, 

 like those of the uterus, of fibrous tissue and plain muscular fibres. 



Uterus. The Uterus (u, c, Fig. 392) is somewhat pyriform, and in 

 the unimpregnated state is about three inches in length, two in breadth 

 at its upper part or fundus, but at its lower pointed part or neck, only 

 about half an inch. The part between the fundus and neck is termed 

 the body of the uterus: it is about an inch in thickness. 



Structure. The uterus is constructed of three principal layers, or 

 coats, serous, fibrous and muscular, and mucous. (1.) The serous 

 coat, which has the same general structure as the peritoneum, covers the 

 organ before and behind, but is absent from the front surface of the neck. 

 (2.) The middle coat is composed of dense connective tissue, with which 



