MAMMARY GLANDS. 



245 



III. Cheiroptera. IV. Insectivora. V. Car- 

 nivora. VI. Cetacea. VII. Pachyder- 

 ma. VIII. Ruminant ia. IX. Edentata. 

 X. Rodentia. 

 Sub-Class. IMPLACENTALIA. 



XI. Marsupialia. XII. Monotremata. 



The aim of the subjoined table is to express 



the mutual affinities and inter-dependencies of 

 the several orders of Mammalia, and the points 

 at which they are most nearly related to the 

 inferior classes of the vertebrate animals. The 

 annectant genera, some of which are extinct, 

 are printed in italics, the orders and classes in 

 Roman capitals. 



BlMANA. 



QUADRUMANA. 



I 



G aleopithecus. 



Lemur. 



I 



Cheiromys. 



Bradypus. 



CHEIROPTERA CARNIVORA. 



t. ; 



INSECTIVORA. 



Didelphys. 



EDENTATA. 



. RODENTIA MARSUPIALIA. 



.MoNOTREMA. 



Pterodactylus. 



AVES. 



Otaria. 

 CETACEA. . . 

 Ichthyosaurus. 

 PISCES. 



Glyptodon. Toxodon. Moschus. 

 .PACHYDERM ATA. . . . RUMINANTIA. 



MAMMARY GLANDS. Syn. Lesglandes 

 mammah-es, Fr., Die Milch, die Brust-drtisen, 

 Germ. These important organs of secretion 

 are the peculiar characteristic of the highest 

 division of the animal kingdom, Mammalia. 

 In a physiological point of view they should 

 be regarded as uterine appendages, as a por- 

 tion of that series of instruments which Na- 

 ture has provided in greater or less number, 

 according to the ultimate perfection of the 

 animal, for its gradual development. Their 

 close proximity to the ovarian apparatus in 

 some Mammalia, the cetacea for instance, and 

 their peculiar structure and function in the 

 Marsupiata, confirm this view of their phy- 

 siological character. It is interesting to trace 

 how gradually they have been removed from 

 their caudal position to the atlantal portion of 

 the body, so that in the human species, where 

 the instincts are subjugated to the control of 

 reason, and the helplessness of the infant has 

 been made the means of moral training to the 

 mother, these organs are brought towards the 

 anterior, the nobler portion of the body. 



It must not, however, be supposed that this 

 change of position is sudden, any more than 

 any other step in the scale of progressive deve- 

 lopment of organized beings. Formerly it was 

 supposed that the re-connection of the ovum to 

 the mother through the medium of bloodvessels 

 collected into a placenta was as universal 

 throughout the class Mammalia as the presence 

 of these glands ; but the careful researches of 

 Professor Owen have proved that the Marsu- 

 piata and most probably some of the Mono- 

 tremata form an exception to this rule. The 

 fact is interesting in reference to the present 

 subject from the greater importance which is 



REPTILIA. 



(R. Owen.) 



given to the mamma in consequence of the ab- 

 sence of this vascular connection, and the addi- 

 tion of accessory structures which are absent in 

 the more perfect mammalia. 



The arrangement of the secreting membrane 

 of mammary glands has been universally found 

 to be vesiculated, the only difference in differ- 

 ent classes of animals consisting in the extent 

 of secreting surface, owing to differences in the 

 size of the cells, and their greater or less concen- 

 tration within a circumscribed space. This 

 vesiculated structure was described in 1751 by 

 Duvernoi* in the hedgehog (Trans, of the 

 Petersburg Academy), and in the human spe- 

 cies it was discovered by Cruikshank, and de- 

 scribed in his work on the absorbent glands, the 

 second edition of which was published in 1790. 

 At page 209 his words are, " The acini are 

 small vesicles like Florence flasks in miniature ; 

 in these, the arteries secreting the milk termi- 

 nate; and from these the excretory ducts, or the 

 tubes carrying off the milk take their origin. 

 The existence of such vesicles has been doubted ; 

 Dr. Hunter doubted till my injections con- 

 vinced him of the fact." He then goes on to 

 explain his method of injecting, and concludes 

 by saying that preparations exhibiting this fact 

 may be seen in the anatomical collection in 

 Great Windmill-street, which he had made 

 fifteen years previously. 



Mu'ller, to whom the above fact was known, 

 states that Mascagni recognised and demon- 

 strated the vesicular ends of the lactiferous 

 tubes and the absence of all direct commu- 

 nication with the bloodvessels, in his Pro- 

 dromo della Grande Anatomia, Firenze, 1819. 



* Miillcr de gland. c. 



