78 ■'•^,Mr. Morgan's Description 



compressing muscles through which they pass ; and it therefore 

 appears more than probable, that whenever the gland is squeezed 

 against the marsupial bone, a greater or less degree of venous 

 congestion, and consequently distention of the part, must be 

 occasioned by the pressure which is made upon the veins 

 through which the blood is returned. That a loaded state of 

 the veins, together with an injection of the lactiferous tubes, 

 will occasion in the marsupial gland of the dead animal an in- 

 crease of size corresponding to that which is found to exist [in 

 the parts during life, I have proved by the experiment of throw- 

 ing an injection of quicksilver into the ducts, and one of water 

 into the blood-vessels, by which process the exact natural form 

 and capacity of the mamma, as it exists during the period of 

 suckling, is artificially produced. Thus the extraordinary dis- 

 tention of the marsupial mammary gland to which I have alluded, 

 is, I conceive, produced in a great measure by an enlargement 

 of the vessels which naturally exist in the part ; but the extra- 

 ordinary distention of the nipple is partly occasioned by a change 

 which takes place in a peculiar vascular structure which enters 

 into the composition of the teat, and which is formed apparently 

 for this particular purpose : for we find immediately beneath the 

 compressing muscle of the teat, that a layer of loose reticular 

 membrane, forming a bed for a congeries of tortuous veins, is 

 interposed between that structure and the central fasciculus of 

 excretory ducts. The vascular sheath by which this central 

 fasciculus is thus inclosed, consists principally of a dense plexus 

 of veins, which are extremely large and numerous in proportion 

 to the size and number of the arteries which accompany them 

 {tab. 8. f. 2. c). So great is the vascularity of this sheath, that in 

 many parts it nearly resembles in appearance the corpus spon- 

 giosum of the penis, and like that part is capable of considerable 

 distention, either by an obstruction to its venous circulation in 



the 



