r60 ANATOMY OF VERTEBRATES- 



CHAPTER XXXIX. 



MAMMARY AND MARSUPIAL ORGANS. 



§ 413. In Monotremata. — In a female Ornithorhynchus, shot in 

 December, and of which the ' corpora lutea ' indicated that she 

 had recently brought forth young, the mammary glands formed 

 an oblong flattened mass on each side of the ventral parietes of 

 the abdomen. Each gland was composed of between one hundred 

 and two hundred elongated subcylindrical lobes, fig. 596, con- 

 verging to a small oval areola, fig. 597, in the abdominal integu- 

 ment, situated between three and four inches from the cloaca, and 

 about one inch from the medial line. The lobes are rounded and 

 enlarged at their free extremities, and become narrower to about 

 one-third from the point of insertion, where they end in slender 

 ducts, fig. 596, a. Almost all the lobes are situated at the outer side 

 of the areola, and consequently converge toward the mesial line of 

 the abdomen : in fig. 596 they are exposed by reflecting outward 

 the skin. Between the gland and the integument the panniculus 

 carnosus is interposed, closely adhering to the latter, but con- 

 nected with the gland by loose cellular membrane. This muscle 

 is here a line in thickness, its fibres are longitudinal, and, sepa- 

 rating, leave an elliptical space for the passage of the ducts of 

 the gland to the areola. On the external surface of the skin, 

 when the hair is removed, this areola can only be distinguished 

 by the larger size of the orifices of the lacteal ducts, compared 

 with those for the transmission of the hairs. The orifices of the 

 ducts thus grouped together form an oval spot, five lines in the 

 long and three in the short diameter. Neither in this nor any 

 other of the many specimens in which I have dissected the mam- 

 mary glands was the surface on which the ducts terminated raised 

 in the slightest degree beyond the level of the surrounding 

 integument. 



In a full-grown female, killed in August, in which two enlarged 

 ovisacs indicated the preparation of ova for impregnation, the 

 mammary gland was reduced to the size given in fig. 598 : diverg- 

 ing tracts of cellular sheaths with fat indicated a previous seasonal 

 enlargement. 



Mercury injected into the substance of a lobe diffused itself 



