On the Female Organs and Flacentation of the Racoon. 287 



placenta resemble ordinary capillaries, whilst those which constitute 

 the foetal portion present an altogether different appearance. 



Foetal Portion of Placenta. — The foetal vessels constituted by far the 

 larger portion of the placenta. Indeed, when sections of the placenta 

 were examined, the entire mass of the organ was apparently composed 

 of these. This I afterwards found was due to the fact that the pro- 

 cesses of maternal tissue in the absence of injection, could not be 

 traced to any great depth in the substance of the organ, and that the 

 delicate capillaries with which they were furnished, were with diffi- 

 culty distinguished amid the much larger vessels of the foetal portion 

 of the placenta. The foetal vessels resembled neither arteries nor veins 

 in the structure of their walls, and yet were of much larger calibre 

 than ordinary capillaries. So far as I am aware, vessels presenting a 

 similar character have only once been previously noticed, and that by 

 Professor Turner in the maternal portion of the placenta of Cholaipus 

 Hoffmanni* With the observations of that anatomist, with regard to 

 the structure of these vessels, my own, except in one or two points, 

 almost entirely agree. When a portion of the placenta of racoon was 

 teased out under the microscope, the vessels in question were seen for 

 the most part to run parallel with one another, from the foetal to the 

 uterine surface of the organ, and could be readily detached in the 

 form of bundles from the cut edge of the placenta. When one of these 

 bundles was farther manipulated, the separate vessels were observed 

 for the most part to be of uniform diameter, although occasionally 

 they presented well-defined enlargements. These in some instances 

 occurred at regular intervals, and gave to the vessel a moniliform 

 character. The vessels freely communicated with one another by means 

 of transverse anastomosing branches of a similar diameter. These 

 transverse anastomosing vessels were given off at somewhat irregular 

 intervals, but for the most part they occurred at intervals which did 

 not much exceed the diameter of the vessels themselves. In conse- 

 quence of this arrangement, transverse- vertical and longitudinal- 

 vertical sections of the placenta presented much the same appearance 

 under the microscope. An examination of the foetal margin of these 

 placental sections showed conclusively that at no spot did the vessels 

 pass beyond this surface of the organ, but that, on the contrary, they 

 invariably turned upon themselves, and re-entered the placenta, and that 

 therefore, so far as their distribution in this direction was concerned, 

 they were clearly confined to the substance of the placenta. With 

 regard to their arrangement at the uterine or papillar surface of the 

 placenta, as already observed, I could not distinguish any clearly- 

 defined limitary membrane bounding their distribution in this direc- 

 tion. At the same time, I may observe, that although very numerous 



* " Trans. Roy. Soc. Edin.," vol. xxvii, p. 79. 



