PLACENTA. 385 



teen in number, converge toward the cord, and unite to form 

 the umbilical vein. Upon the uterine surface, are numerous 

 oblique openings of the veins which return the maternal 

 blood to the uterine sinuses. There are also numerous small 

 spiral arteries, which pass into the substance of the organ to 

 supply blood to the maternal portion. These are the " curl- 

 ing arteries," described by John Hunter. 1 



If we inject the umbilical arteries, the fluid is returned 

 by the umbilical vein, having passed through the vascular 

 tufts of the foetal portion of the placenta. According to 

 Farre, the small arteries and the veins of the villi at first 

 communicate through a true capillary plexus ; but, toward 

 the end of pregnancy, the capillaries disappear, leaving loops 

 of vessels, " simple, compound, wavy, or much contorted, and 

 ip parts varicose." 3 



According to the recent researches of Winkler, there are 

 three kinds of foetal villi : 1. Those which terminate just 

 beneath the chorion, without penetrating the vascular lacu- 

 nae. 2. Longer villi, which hang free in the lacunae. 3. Long, 

 branching villi, which penetrate more deeply into the placenta, 

 some extending as far as its uterine surface. 3 "Winkler does 

 not admit the existence of perivascular spaces in the foetal 

 tufts, which have been described by Reitz. 4 



The formation of the great vascular lakes of the maternal 

 portion of the placenta has already been described. 5 These, 

 according to Winkler, present numerous trabeculae, which ex- 

 tend from the uterine to the foetal surface ; and, between these 

 trabeculse, are numerous exceedingly delicate transverse and 



1 HUNTER, On the Structure of the Placenta. Observations on Certain Parts 

 of the Animal (Economy, London, 1792, p. 171. 



3 FARRE, op. tit. Cyclopaedia of Anatomy and Physiology, London, 1859, 

 vol. v., Supplement, p. 718. 



8 WINKLER, Zur Kentniss der menschlichen Placenta. Archiv fur Gynaeko- 

 logie, Berlin, 1872, Bd. iv., S. 249. 



4 WINKLER, op. cit., S. 253. 



REITZ, in STRICKER, Manual of Human and Comparative Histology, The New 

 Sydenham Society, London, 1873, vol. iii., p. 496. 

 6 See page 378. 



