638 



HANDBOOK OF PHYSIOLOGY. 



layer. It is said by some that the superficial follicles as they ripen be- 

 come more deeply placed in the ovarian stroma; and, again, that as they 

 increase in size, they make their way towards the surface (Fig. 425). 



When mature, they form little prominences on the exterior of the 

 ovary, covered only by a thin layer of condensed fibrous tissue and epi- 

 thelium. Only a few follicles ever reach maturity. 



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 pe^'od, 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 



FIG. 



FIG. 428. 



FIG. 427. Ovum of the sow. 1, germinal spot; 2, germinal vesicle; 3, yolk; 4, zona pellucida; 

 5, discus proligerus; 0, adherent granules or cells. (Barry.) 



FIG. 428. -Germinal epithelium of the surface of the ovary of five days' chick, a, small ovo- 

 blasts; 6, larger ovoblasts. (Cadiat.) 



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

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



I. The Fallopian Tubes or Oviducts. 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 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 oifiwibricB, one of which, longer than 

 the rest, is attached to the ovary. The canal by which each tube is tra- 

 versed 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 fim- 

 brise. Externally, the Fallopian tube is invested with peritoneum; in- 

 ternally, its canal is lined with mucus membrane, which is apt to be 

 thrown into numerous folds, covered with ciliated epithelium: between 

 the peritoneal and mucous coats, the. walls are composed, like those of 



