Sect. XXXVIII. 2. i. OF BLOOD. 369 



cavities or lacunae formed on that fide of the placenta, which is 

 in contact with the uterus ; thofe cavities or cells are filled wit U 

 blood from the maternal arteries, which open into them ; which 

 blood is again taken up by the maternal veins, and is thus per- 

 petually changed. While the terminations of the placental ar- 

 teries and veins are fpread in fine reticulation on the fides of 

 thefe cells. And thus, as the growing fetus requires greater 

 oxygenation, an apparatus is produced reiembling exactly tne 

 air-cells of the lungs. 



In cows, and other ruminating animals, the internal fur face 

 of the uterus is unequal like hollow cups, which have been 

 called cotyledons ; and into thefe cavities the prominences of 

 the numerous placentas, with which the fetus of thofe animals 

 is furnifhed, are inferted, and ftnctly adhere ; though they may 

 be extracted without effufion of blood. Thefe inequalities of 

 the uterus, and the numerous placentas in confequence, feem to 

 be defigned for the purpofe of expanding a greater furface for 

 the terminations of the placental veflels for the purpofe of re- 

 ceiving oxygenation from the uterine ones ', as the progeny of 

 this clafs of animals are more completely formed before their 

 nativity, than that of the carnivorous clafTes, and muft thence in 

 the latter weeks of pregnancy require greater oxygenation. 

 Thus calves and lambs can walk about in a few minutes after 

 their birth ; while puppies and kittens remain many days with- 

 out opening their eyes. And though on the reparation of the 

 cotyledons of ruminating animals no blood is effufed, yet this is 

 owing clearly to the greater power of contraction of their ute- 

 rine lacunae or alveoli. See Medical EiTays, Vol. V. page 144. 

 And from the fame caufe they are not liable to a fanguiferous 

 menftruation. 



The necefiity of the oxygenation of the blood in the fetus is 

 farther illuftrated by the analogy oi the cluck in the egg ; which 

 appears to have its blood oxygenated at the extremities of the 

 VelTels furrounding the yolk 5 w r hich are fpread on the air-bag 

 at the broad end of the c^g^ and may abforb oxygene through- 

 that moift membrane from the air confined behind it ^ and which 

 is (hewn by experiments in the exhaulled receiver to be change- 

 able through the iheil. See Phytoiogia, Sect. III. 



This analogy may even be extended to the growing feeds of 

 vegetables •, which were (hewn by Mr. Schcele to require a reno- 

 vation of the air over the water, in which they were confined 

 Many vegetable feeds are furrounded with air in their pods or 

 receptacles, as peas, the fruit of fi^phylea, and lichnis veficaria \ 

 but it is probable, that thofe feeds after they are ihed, as w r ell as 

 the fpawn of iill], by the foliation of the former on or near the 



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