FCETAL NUTRITION: THE PLACENTA 



435 



maternal part of the burr appears to be digested and absorbed by the 

 trophoblast. The greater activity of the foetal ectoderm in the deer 

 is also shown by the destruction of the epithelium over the whole 

 tmrface of the uterus (Strahl l ). 



FIG. 118. Histology of the placenta in the cow and sheep. (From Jenkinson, 

 Vertebrate Embryology, Oxford, at the Clarendon Press.) 



1. Festal and maternal tissues in a cotyledon, tr, Trophoblast of a villus ; the 



cells are absorbing fat (black). In the trophoblast are binucleate cells. 

 Behind it are the connective tissue and blood-vessels of the allantois. 

 ep, Uterine epithelium lining a crypt. Fat secretion is going on, the ends 

 of the cells with fat globules being pinched off and thrown into the crypt's 

 lumen. Below the epithelium are maternal capillaries and connective tissue. 



2. Columnar trophoblast cells form between the bases of the cotyledonary villi. 



The cells contain ingested matter (corpuscles, nuclear, and cell debris). 



3. Ingestion of extravasated maternal corpuscles by the trophoblast in the 



sheep. The cells contain pigment besides corpuscles. 



4. Deposition of pigment derived from haemoglobin of ingested corpuscles in 



trophoblast cells of cow. The pigment granules (black) are deposited in 

 irregular masses. 



In addition to blood, the uterine milk contains fat in large 

 quantities. Before pregnancy it may be demonstrated in the sub- 

 epithelial leucocytes which later migrate to the surface. Fat globules 

 are also contained in large amount in the epithelial cells of the 



1 Strahl, "Ueber die Semiplacenta multiplex von Cervus elaphus," Anat. 

 Hefte, H. xciii., 1906. 



