. Evolution and disease . Fig. 91.—The inguinal region of a Lamb, showing the cutaneousrecesses in its groin. nature of the secretion is not very great. The sebaceousvariety furnishes a fatty unctuous substance ; mammae,a natural emulsion known as milk, consisting of oilglobules suspended in fluid, containing various salts anda proteid body, casein, with a small but variable propor-tion of albumen. 174 EVOLUTION AND DISEASE. As all cutaneous recesses exhibit a marked tendencyto develop glands, the large size and abundance of themammary glands within the marsupium of opossumsreceives an explana
. Evolution and disease . Fig. 91.—The inguinal region of a Lamb, showing the cutaneousrecesses in its groin. nature of the secretion is not very great. The sebaceousvariety furnishes a fatty unctuous substance ; mammae,a natural emulsion known as milk, consisting of oilglobules suspended in fluid, containing various salts anda proteid body, casein, with a small but variable propor-tion of albumen. 174 EVOLUTION AND DISEASE. As all cutaneous recesses exhibit a marked tendencyto develop glands, the large size and abundance of themammary glands within the marsupium of opossumsreceives an explanation. A comparison of the inguinal pouches in the sheep. Fig. 92.—The marsupium of a Phalanger {Phalangista oricnfulis)opened to show the number of teats. with the marsupium of the phalangers, &c., is instructive,as it indicates in a significant manner the mode by whicha specialized bag, or marsupium, may have originated,besides throwing light on the number of teats it ATAVISM. 175 By far the most remarkable situation in which milk-glands arise, is in the interior of some peculiar skin-con-taining tumours of the ovary. I have traced every stagefrom a sebaceous gland to a nipplcd mamma, furnishingmilk, in such tumours—a situation in which it wouldpuzzle even Paley to imagine a useful purpose. These facts indicate clearly enough that a mammamay make its appearance in any situation of the bodyif the favouring conditions exist—, a cutaneousrecess abundantly supplied with sebaceous glands, andpreferably on the ventral or protected aspect of thebody ; warmth and moisture appearing to favour theirdevelopment. The careful
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectabnormalitieshuman
