90 CARNEGIE INSTITUTION OF WASHINGTON. 



muscle-coats of the bladder and, extending down, partially encircle 

 the upper end of the urethra. As regards the trigonal muscle, Dr. 

 Wesson shows that its origin and nervous control are different from 

 those of the rest of the bladder musculature and that it is probably 

 independent in its contraction and relaxation. Embryologically, it is 

 of mesodermal origin, whereas the fundus is of ectodermal origin. 

 Certain definable muscular structures about the neck of the bladder, 

 which have hitherto not been recognized, such as the external and 

 internal arcuate muscles of the vesicle orifice, are described by Dr. 

 Wesson. With anatomical data of this character we may expect to 

 arrive at a satisfactory explanation for the various phenomena of 

 micturition. 



Cyclic Changes in Ovary and Uterus. 



An important contribution to our knowledge regarding the changes 

 in the mammalian ovary and uterus during the successive events of 

 the reproductive cycle has been made by Dr. G. W. Corner. Through 

 the cooperation of the manager of a large piggery, operated as a garbage 

 disposal plant for the City of Baltimore, Dr. Corner was able to obtain 

 the internal genitalia of pregnant and non-pregnant pigs in which the 

 oestrous period had been observed at all stages of the cycle. From a 

 histological study of this material he has correlated the anatomical 

 changes in the uterus and ovary that underlie ovulation and the 

 mechanism of implantation. Of the various domestic mammals, the 

 pig possesses certain advantages for the study of the reproductive 

 cycle and reduces the problem to the simplest possible terms. The 

 oestrus is periodic, frequent, and conspicuous; ovulation is spontaneous; 

 the litters are large; the ovaries are uncomplicated as compared with 

 those of rodents; and finally, the uterine mucosa is of the nondeciduate 

 type, with a simple, diffuse placenta. Dr. Corner's observations have 

 been published in three separate communications, from one of which I 

 am reproducing a diagram showing the periodic growth of the ovarian 

 follicles and the consequent formation and regression of the corpora 

 lutea. (See fig. 1.) 



It will be seen that the cycle is 21 days in length and that ovulation 

 occurs during oestrus. It is also of interest to note that the corpus 

 luteum remains in full development from the seventh to the fifteenth 

 day, long enough to cover the period of attachment of the embryos. 

 If no embryos are present, the corpora lutea degenerate at about the 

 fifteenth day. It has been found by Dr. Corner that during the growth 

 period of the corpus luteum the uterus undergoes histological changes 

 which culminate, at the eighth to tenth day, in marked epithehal 

 activity, with the appearance of an active serous secretion. At this 

 time the embryos, in case the ova are fertilized, are still unattached 

 and are being shifted into position for implantation. From the tenth 

 to the fifteenth day (the period of implantation) further changes in 



