76 Mr. Morgan's Description 



until by the contraction of the latter the ducts become dis- 

 tended, no resistance is offered in the direction of the longitu- 

 dinal fibres of the muscle which incloses them ; and we conse- 

 quently find, that when the marsupial teat is empty and tlaccid, 

 its contraction (which can be easily felt in the living animal) 

 diminishes the part to one-fourth of its size when in the distended 

 state ; for when empty the teat is drawn up, and the skin which 

 covers it becomes loose and corrugated. When, however, the 

 teat is distended, the contraction of the muscle would of course 

 tend to produce a considerable degree of pressure upon the ves- 

 sels which it incloses. 



Having thus endeavoured to prove, that a forcible compres- 

 sion of the gland and teat is necessarily occasioned by the con- 

 traction of their surrounding muscular investments, and that by 

 this compression the excretory vessels must be emptied of their 

 contents ; having also mentioned the probable necessity for this 

 provision in the mother, as indicated by the condition of the 

 young, I shall now conclude my account of the mammary organs 

 by describing some other structures which enter into the com- 

 position of the teat and gland. It will be necessary, however, 

 that I should first notice a peculiar and singular change in these 

 structures, which 1 have observed to occur in the living animal, 

 and which is, I conceive, in a great measure dependent upon 

 the existence and functions of other parts which yet remain 

 undescribed. 



The change to which I allude consists in an extraordinary 

 distention or enlargement of the marsupial mammary gland and 

 teat, which is constantly found to take place during the time the 

 young is engaged in the act of sucking. This distention is con- 

 siderably greater than any which could possibly arise from the 

 most forcible injection of the lactiferous tubes ; and I have 

 clearly ascertained, by repeated and careful examinations of 



the 



