196 
CHAS. H. O’OONOGHUE. 
the ramifying mammary tubules of which the adult gland is 
composed, and from which the secretory alveoli develop. 
At a later stage of development than is described above, the 
hollow of the tubules extends upwards along the solid cord, 
which is thus transformed into a duct, and comes to open 
into the upper end of the lumen of the follicle. 
From this condition ot‘ the gland and teat the transition to 
the adult form is fairly straightforward, and may be con- 
veniently divided into three stages : (1) The strong hair with 
its follicle and outgrowing sebaceous gland completely dis- 
appears. This, of course, leaves the duct of the mammary 
gland opening directly into the teat pocket. (2) The 
mammary tubules increase greatly in length, and become 
more ramified. (3) The original epidermal invagination, 
forming the teat pocket, is everted to form the definitive teat. 
The Adult Gland. 
The resting pouch in the adult is a well-marked, though 
shallow, almost circular depression, containing as a rule six 
teats. This number, however, is subject to slight variation, 
for in the thirty pouches I examined, one (No. 3) had only 
five teats, with no trace of the sixth, another, (No. 13) had 
seven, and two (Nos. 6 and 7) had eight. The teats are 
arranged on either side of a slightly raised ridge occupying 
the middle line, and are usually situated nearer to the anterior 
end of the pouch. On the apex of the teat open a number of 
main milk-ducts (normally six, see fig. 6), which run down 
some way below the skin before branching into a large 
number of ramifying mammary tubules. The lining of the 
main ducts running through the teat, from their external 
openings up to the point at which they branch, consists of a 
stratified epithelium four or five cells deep (fig. 12). The 
branched mammary tubules of the resting gland, on the other 
hand, are lined by a double layer of cells, similar in appear- 
ance to those already described in the pouch young. 
The skin lining the pouch is especially characterised by 
