INTEGUMENT 



37 



a papilla, while the surrounding skin remains almost on a level 

 with the rest of the integument (c). In the latter case, therefore, 

 there is an e pagination of the mammary pocket, and the teats 

 may be described as secondary or true (Marsupials, Rodents, 

 Lemurs, Monkeys, and 

 Man), and in the former 

 as primary or pseudo- 

 teats (Carnivores, 

 Pigs, Horses, and Ru- 

 minants). The latter 

 condition is already in- 

 dicated in certain Mar- 

 supials (e.g. Phalangista 

 vulpina). 



The teats are often 

 situated in two nearly 

 parallel rows along the 

 ventral side of the 

 thorax and abdomen 

 which slightly converge 

 towards the inguinal 

 region (e.g. Carnivores, 

 Pigs) : in other cases 

 they may be restricted 

 either to the inguinal 

 (Ungulates and Ceta- 

 ceans) or to the thoracic 

 region (Sloths, Manis, 

 Elephants, Sirenia, 

 many Lemurs, Cheirop- 

 tera, and Primates) : 

 while in others, again, 

 they may be axillary or 



[G. 29. DIAGRAMMATIC REPRESENTATIONS OF 

 THE EARLY DEVELOPMENT OF THE LEADING 

 TYPES OF MAMMARY GLANDS. (Modified from 

 G egenbaur.) 



abdominal, or they may 

 occur in various com- 

 binations of all these 



, first or undifferentiated (mammary pocket) 

 stage ; , stage of the pseudo- (primary) teat ; 

 C, stage of the true (secondary) teat ; rf, mam- 

 mary canal ; f.g, glandular area; gl, mammary 

 glands ; v, rim (or rampart) of the glandular area. 



regions. 



The number of teats varies greatly : there may be as few as 

 one pair, or as many as eleven pairs (Centetes) : in general, their 

 number corresponds to that of the young produced at one 

 birth. 



Not infrequently, 'supernumerary or accessory mammae and 

 teats can be recognised (e.g. in Sheep and Cattle), and there may 

 be indications in the foetus of a greater number of teats than that 

 which occurs in the adult : thus in the embryo of Whalebone- 

 Whales there are eight pairs, while the adult possesses only a 

 single pair on either side of the vulva. Cases of such a hyper- ' 

 mastism and hyperthelism are also well known in the human 



