SIR WM. TURNER ON THE PLACENTATION OF HALICORE DUGONG. 649 



with the inner wall of the sac of the allantois, which together with the fluid in that sac 

 separated the amnion from the endochorion (see woodcut, p. 660). 



Both the endochorion and the allantois enveloping the amnion were vascular, and 

 the vessels were derived from the umbilical cord. The cord was undivided for from 

 3 to 4 inches beyond the belly of the foetus, and in its undivided part it was invested by 

 the amnion. A transverse section made through it immediately before its division 

 showed eight vessels, four arteries and four veins, each of which was surrounded by 

 delicate gelatinous tissue. As soon as the cord reached the allantois it divided into 

 four branches, each of which contained an artery and a vein. Each branch immedi- 

 ately became invested by a fold of the allantois, by means of which it was conveyed 

 to the inner surface of the placenta opposite the belly of the foetus. These folds were 

 of considerable length and breadth, and were continuous with that layer of the allantois 

 which enveloped the amnion. They and the branches of the cord situated along their 

 free borders had floated in the fluid of the allantoic sac. The cord was spirally twisted 

 before its division, each of its branches also was tortuous, and a similar character also 

 was seen in the vessels as they ramified on the inner surface of the placenta. An 

 attempt was made to inject the umbilical vessels with gelatine and carmine, which was 

 successful as far as the large trunks were concerned. Many of the vessels ramifying 

 on the inner surface of the placenta were also filled. The injection had not penetrated 

 into the capillaries within the villi, though it was not unusual to see villi stained with 

 carmine from the injecting material. 



The vascularity of the chorion was not limited to the placental zone, for a number 

 of vessels, both arteries and veins, passed beyond each margin of the placenta as far as 

 the corresponding pole of the chorion. To some extent the injection had penetrated 

 into these vessels, but even when not injected they could be readily seen to ramify in 

 the endochorion lining the non-zonary parts of the chorion. 



The villi in the placental zone varied in length. Comparatively a few were on the 

 average T 7 u^ ns mcn (18 mm.) long, but the great majority, many thousands in number, 

 were from -j^ths to T ^ths inch (8 to 10 mm.). The stems of the villi were cylindriform 

 and filamentous, but those of the longer villi were thicker and tougher than the stems 

 of the shorter villi. The shorter villi branched about x^th inch (2*5 mm.) or a little more 

 from their origin from the chorion, and gave rise to two, three, four, or more rarely 

 five branches, which arose in proximity to each other (fig. 3). They were much smaller 

 than the stems from which they sprang, and after a course of about T %ths inch they not 

 unfrequently bifurcated, and the branches of bifurcation ended in short terminal buds. 

 These shorter villi had been lodged in the shorter crypts which formed the spongy 

 surface of the uterine mucosa, and had been drawn out of the crypts before I opened 

 the uterus. 



The longer villi were more firmly attached to the maternal zone, so much so indeed 

 that they had been torn away from the chorion, and their free ends were implanted in 

 the wider and deeper crypts described in my account of the maternal placenta. The free 



VOL. XXXV. PART II. (NO. 17). 5 M 



