REPRODUCTION 519 



difference of opinion as to whether the rupture of the Graafian 

 follicle occurs most frequently immediately before the appearance 

 of the menstrual flow, or towards its close; but the preponderance 

 of evidence favors the latter view. The menstrual process probably 

 is a special preparation of the womb for the reception of an embryo 

 and its nourishment. There is, however, evidence that ova arc 

 occasionally discharged at other than the regular monthly periods 

 of ovulation and may be fertilized and cause a pregnancy. 



Pregnancy. When the mulberry mass reaches the uterine cav- 

 ity the mucous membrancc lining the latter grows rapidly and 

 forms a new, thick, very vascular lining to the womb, known as the 

 decidua. At one point on this the morula becomes attached, the 

 decidua growing up around it. As pregnancy advances and the 

 embryo grows, it bulges out into the uterine cavity and pushes 

 before it that part of the decidua which has grown over it (the 

 decidua reflexa) ; at about the end of the third month this coalesces 

 with the decidua lining the opposite sides of the uterine cavity so 

 that the two can no longer be separated. That part of the decidua 

 (decidua serotina) against which the morula is first attached sub- 

 sequently undergoes a great development in connection with the 

 formation of the placenta (see below). Meanwhile the whole 

 uterus enlarges; its muscular coat especially thickens. At first the 

 organ still lies within the pelvis, where there is but little room for 

 it; it accordingly presses on the bladder and rectum (see Fig. 152) 

 and the nerves in the neighborhood, frequently causing consider- 

 able discomfort or pain; and, reflexly, often exciting nausea or 

 vomiting (the morning sickness of pregnancy). Later on, the preg- 

 nant womb escapes higher into the abdominal cavity, and although 

 then larger, the soft abdominal walls more readily make room for 

 it, and less discomfort is usually felt, though there may be short- 

 ness of breath and palpitation of the heart from interference with 

 the diaphragmatic movements. All tight garments should at this 

 time be especially avoided; the woman's breathing is already suffi- 

 ciently impeded, and the pressure may also injure the developing 

 child. Meanwhile, changes occur elsewhere in the Body. The 

 breasts enlarge and hard masses of developing glandular tissue 

 can be felt in them; and there may be mental symptoms: depres- 

 sion, anxiety, and an emotional nervous state. 



During the whole period of gestation the woman is not merely 



