of the Mammary Organs of the Kangaroo. 75 



The smaller gland appeared somewhat more vascular than 

 that which I had before examined in the younger animal, and 

 was connected by a similar arrangement of ducts with the upper 

 and smaller nipple {tab. 8./. 1. a.). From the larger marsupial 

 mammary gland about twenty excretory ducts are sent off, these 

 being closely connected together by reticular membrane, and 

 inclosed in a sheath, (forming, as I have stated, a sort of fasci- 

 culus or cord,) are continued to their termination at the extre- 

 mity of the nipple in nearly a straight line. In its course from 

 the gland, this plexus cf ducts first passes between the skin of the 

 pouch and the abdominal muscles as far as the base of the mar- 

 supial teat, at which part it enters the teat, and is continued to its 

 extremity, where each duct terminates by a separate opening. A 

 sheath of longitudinal muscular fibres closely envelops this fas- 

 ciculus of ducts throughout its whole extent ; and at the point of 

 junction with the gland, these muscular fibres are expanded over 

 the surface of that organ, to nearly the whole of which they are 

 attached by cellular connections (tab. 8.f. 1. b.). 



The use of this muscle is to draw up and shorten the teat, when 

 its ducts are emptied, or to compress that part when this retrac- 

 tion is prevented by a distended state of its vessels : whenever, 

 therefore, the lactiferous tubes are filled by injection from the 

 mammary gland, and the part becomes distended, this muscle 

 considerably facilitates the transmission of the secreted fluid 

 through the teat by compressing the ducts, and thus squeezing 

 their contents towards the extremity of the nipple. Thus the 

 lactiferous tubes within the mammary gland, and the excretory 

 vessels which are sent oft' from those tubes through the teat, are 

 furnished by Nature with precisely the same muscular apparatus 

 for the ejection of their contents. 



The compressing muscle of the teat, however, is only capable 

 of performing this office when assisted by that of the gland ; for 



L 2 until 



