REPRODUCTION. 



653 



12 to 1 8 cm. in length, situated between the rectum and bladder. 

 It extends from the surface of the body to the brim of the pelvis, 

 and embraces at its upper extremity the neck of the uterus. 



Ovulation. After the establishment of puberty a Graafian follicle 

 develops and ripens or matures periodically, usually every twenty- 

 eight days. During the time of maturation the follicle increases in 

 size, from an augmentation of its fluid contents, and approaches the 

 surface of the ovary, where it forms a projection varying from 6 

 to 12 mm. in size. When maturation is complete the vesicle rup- 



FIG. 319. OVUM OF A Cow. i. Zona pel- 

 lucida. 2. Cytoplasm, vitellus. 3. Nu- 

 cleus, germinal vesicle. 4. Nucleolus, 

 germinal spot. 5. Corona radiata. The 

 radial striation of the zona pellucida 

 can not be seen. (Stohr.} 



9\ 



FIG. 320. FRONTAL SECTION 

 OF THE UTERUS, i. Cav- 

 ity of the body. 2, 3. 

 Lateral walls. 4, 4. Cor- 

 nua. 5. Os internum. 6. 

 Cavity of the cervix. 7. 

 Arbor vitae of the cervix. 

 8. Os externum. 9. Va- 

 gina. (Sappey.) 



tures, and the ovum and liquid contents are discharged. The ovum, 

 by a mechanism not fully understood, is received by the fimbriated 

 extremity of the Fallopian tube and enters its cavity. The ovum is 

 then transferred through the tube by the peristaltic contraction of 

 its muscle- fibers and by the action of the cilia of its lining epithelium. 

 The time occupied in the transference of the ovum from the ovary 

 to the interior of the uterus has been estimated to be from four to 

 ten days. 



Either at the time, or very shortly after, its discharge from the 

 follicle, the ovum, and more especially the nucleus, undergoes a series 

 of histologic changes which eventuates in an extrusion of a portion 



