15 



to Dr. J. L. Crenshaw of Charlottesville, Va. The specimen was 

 removed from the uterus immediately after hysterectomy and sent to 

 me in a 5 7o formalin solution. The chorionic vesicle had been opened 

 but the amnion and yolk sac were left intact (Fig. 1). The specimen 

 was transferred to 95 % alcohol after several hours. Both embryo and 

 sac were stained in toto 

 with borax carmine, im- 

 bedded in paraffine and 

 sectioned at 10 microns. 

 The stain proved rather 

 faint and some of the slides 

 were placed for several 

 seconds in a saturated 

 aqueous solution of saffranin. 

 This yielded a very satis- 

 factory differential stain. 

 Microscopic study revealed 

 a very excellent state of 

 preservation of the entire 

 specimen including the 

 chorionic villi. Comparisons 

 will be made with the 

 structure of the umbilical 

 vesicle of a 9,2 mm human 

 embryo, previously described (24), and several of the illustrations are 

 from this specimen. The umbilical vesicle of this younger embryo was 

 at the height of its development. The changes consequent upon a slight 

 increase in age as seen in the older specimen are instructive. 



Part I. 

 Macroscopic Appearance and Comparisons. 

 The umbilical vesicle has an almost spheric form, but is drawn 

 out into a slender tube at its proximal pole where it passes into the 

 pedicle. It thus has roughly the pyriform shape as ordinarily described. 

 The surface of the vesicle is slightly roughened due to the tubules 

 and blood-vessels in the outer surface of the wall. Its dimensions are 

 6 mm X 4 mm, an increase of 1 mm in both axes over that of the 

 9,2 mm embryo. This indicates growth for at least a week beyond 

 the first month (30 days). Meyer's (33) figures given for 18 vesicles 

 in the collection of Dr. Mall of John Hopkins University show con- 

 siderable variation in size among the umbilical vesicles of embryo 



Fig. 1. Photograph of 13 mm human em- 

 bryo, showing amnion, umbilical vesicle and open 

 chorionic vesicle. Made by Mr. Fkank P. Smakt, 

 University of Virginia. 



