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Show 108 ON CLASSIFICA'l'ION. placenta in all genera ,~·hich have been examined (except the Polecat, according to Von Baer) has the form of a complete zone, Fig. 43. \ Azz/~ Fig. 43.-Fretal kitten, with its membranes and placenta. The latter is seen from within, the chorion and allantois being open and everted.-Am, amnion ; AU, allantois; Pl, placenta; Um, umbilical vesicle. (From a preparation in the ~1 usenm of the Royal College of Surgeons.) or broad girdle, surrounding the middle of the chorion and leaving the poles bare (E ig. 43). Thus l\ian; the Apes, or so called Quadrumana; the Insectivora; the Oheiroptera; the ltodentia, to which the lowest apes present so many remarkable approximations; and the Carnivora (united into one group with the Insectivora by Cuvier) are all as closely connected by their placental structure as they are by their general affinities. With the Pig, on the other hand, all the Artiodactyla, all the Perissodactyla (save one, taking the group in its ordinarily received sense) and all the Cetacea which have been studied, agree in developing no decidua, or, in other words, in the fact that no vascular maternal parts are thrown off during parturition. Rut considerabl differ nee· aro ob ·erved in the details THE PLACENTJE OF RUMINANTS. 109 of the disposition of the footal villi, and of the parts of the uterus which receive them. Thus, in the Horse, Camel, and Cetacea the villi are scattered, as in the Pig, and the placenta is said to be d~ffuse; while, in almost all true Ruminants, the fmtal Fig. 4-4. Fi~. 44-.-Uterus of a Cow in the middle of pregnancy laid open.- V, vagina; U, uterus ; Cit, chorion; Cl, uterine cotyledons; C2, fretal cotyledons (after Colin). Fig. 45. Fig. 4~.-A. Horn of the Uterus of a pregnant Ewe, laid open to show, Ch, the chorion; With Co, the cotyledons. 13. Diagrammatic section of a Cotyledon.- U, uterine w~ll; Col, uterine cup of the cotyledon ; Co2, chorionic villous tuft of the cotyledon. 1 P'rom a preparation in the Museum of the Royal College of Surgeons.) |
