FOETAL NUTRITION: THE PLACENTA 467 



foetal kidneys, but does not traverse the maternal placenta and enter 

 the maternal circulation. 



Mouse. The fertilised ova of the mouse reach the uterine cavity 

 on the third day, and segmentation is completed one day later. The 

 zona pellucida has by this time disappeared, and fixation of the 

 ovum to the uterus can be quickly attained. Each blastocyst comes 

 to rest in an anti-mesometrial groove. At first spherical, it becomes 

 ovoid on the sixth day, with the long axis perpendicular to ; the long 

 axis of the uterus. One pole is turned towards the mesometrium and 

 is composed of several layers of cells, while the opposite pole is single- 

 layered. It is nourished by the glandular secretion, and perhaps also 

 by a transudate, in which, however, leucocytes are not present. 



The connective tissue of the mucosa shows a thickening at the 

 point where a blastocyst rests. The epithelium degenerates as 

 the result of contact with the foetal ectoderm (Duval 1 ), or of 

 pressure by the proliferated connective tissue cells which interferes 

 with the nutrition of the epithelium (Burckhard 2 ), More probably 

 it is not mechanical, as the change begins first at the mouth of the 

 groove, i.e. at the point of first contact with the ovum (Kolster 3 ). 

 In the cells the chromatin clumps on the inner surface of the nuclear 

 membrane, the cell boundaries disappear, and a symplasma is formed 

 which later becomes broken up into nuclear and cellular fragments. 

 Fat globules, which are present in the epithelium of the non-pregnant 

 uterus, are found in the detritus and also in the fostal ectoderm. 



With the destruction of the epithelium appears the first sign of 

 decidual formation. The connective tissue cells increase in size and 

 displace the glands ; the capillaries dilate irregularly, and at places 

 form sinuses. 



On the sixth day the ectoplacental cone is formed by a proliferation 

 of the ectoderm at the mesometrial pole of the blastocyst. It plugs 

 the opening between the crypt and the lumen of the uterus. At the 

 same time the lips of the crypt are gradually brought nearer to each 

 other by the swelling of the tissues, and at the end of the seventh 

 day they fuse and cover the ectoplacenta. In this way the ovum is 

 completely shut off in -a decidual cavity, the " Eikammer," from the 

 uterine lumen. The roof of the chamber forms the primary decidua 

 retiexa, and it is gradually thickened by a decidual deposit. In it 

 new blood-vessels are developed, and they form a specially rich 

 vascular network. 



1 Duval, "Le Placenta des Rongeurs," Jour, de I'Anat. et de la Phys., 1891. 



2 Burckhard, " Die Implantation des Eies der Maus in die Uterinschleim- 

 haut," Arch. f. mikr. Anat., vol. Ivii., 1901. 



3 Kolster, " Zur Kenntnis der Embryotrophe beim Vorhandensein einer 

 Decidua Capsularis," Anat. ffefte, vol. xxii. 



