MAMMARY GLANDS IX MUTILATA. 



777 



usually a tussock surrounded by water, like a lake-dwelling : the 

 number of young is from four to seven. 



416. In Mutilata. In Cetacea the mammary glands, two in 

 number, are oblong, narrow, flat bodies, lying between the dermal 

 and abdominal muscles, with the subcutaneous blubber between 

 them and the skin. The requisite mass of glandular substance 

 at the suckling season is obtained by horizontal extent, not by 

 thickness, so that they do not project, or interfere with the requi- 

 site shape of the natatory animal. Each gland has a principal duct 

 running in the middle through the whole length of the gland, and 

 collecting the smaller lateral ducts, which are made up of the still 

 smaller ones. ( Some of these lateral branches enter the common 

 trunk in the direction of the milk's passage, others in the contrary 

 direction, especially those nearest to the termination of the trunk 

 in the nipple. The trunk is 

 large, and appears to serve as 

 a reservoir for the milk : ' 1 it is 

 continued from the hinder end 

 of the gland, and terminates in 

 a nipple concealed in a cleft, fig. 

 608, c, one on each side of the 

 vulva, a, and toward the vent, b. 



607 



608 



Mammary cleft dilated, exhibiting the nipple 

 and its orifices, Porpoise. CCLXXXIII". 



Position of mammary clefts, Porpoise. 



CCLXXXIII". 



The lateral portions of the cleft are composed of parts looser in 

 texture than the common skin, which is probably to admit of the 

 elongation or projection of the nipple. On the outside of this 

 there is another small fissure, which gives greater facility to the 

 movements of all these parts. 



The nipple itself, shown by dilating the mammary fossa in 

 fig. 607, is perforated by numerous lacteal ducts. Hunter thus 

 alludes to the unusual circumstances under which the act of 



1 xciv. p. 392. 



