GENERATIVE SYSTEM. 309 



each of vvliich masses is composed of a number of lobules closely 

 compacted and united together : a composition altogether that 

 accounts for the loose or knotty feel which the gland is well 

 known to possess. These insulated lobulous portions receive 

 small arteries in numbers from the parent arterial trunk, from 

 whose terminations arise (we do not precisely know in what 

 manner) the tuhuli lactij'eri. These numberless little tubules, 

 by repeatedly conjoining one with another, become at length 

 several demonstrable canals, radiating from every part to as- 

 semble in the teat : still uniting one with another in their course, 

 and occasionally dilating into considerable reservoirs for holding 

 the secretion. The lactiferous conduits are continued through 

 the substance of the teat, wherein during its relaxation they are 

 so serpentined or coiled, that milk cannot spontaneously flow 

 from them ; but in the distended state of that body, or when it is 

 drawn out in the act of suction or milking, these ducts are ren- 

 dered straight, and the milk, either in consequence of internal or 

 external pressure, readily runs out. 



THE PAPILLA, teat, or dug, depending from the most 

 prominent part of either udder, near its middle, is conical, black, 

 and hairless. Its tegumental sheath is of the same description 

 as that covering the bag from which it is derived, only it is per- 

 forated at the apex by three holes, to give issue to the milk ; and 

 underneath this is a second tunic, which comes from the elastic 

 ligamentous covering, also of the gland. Through these open- 

 ings (one of which is commonly conspicuous for its size) the 

 milk is discharged from the conduits of the lactiferous tubes. 

 When the udder becomes charged with milk, it flows into the 

 teat, and distends it ; and as the secretion is probably influenced 

 in animals (as it is in the human subject) by anxiety for the 

 young, the animal evinces this feeling by a state of distention 

 of these parts. The papilla, as has been remarked before, en- 

 larges during the season of lactation, and it does not afterwards 

 recover its original volume so nearly as the udder itself does: a 

 fact, I repeat, that may lead, when the first sign is wanting, to 

 the discovery of mares that have bred. 



Sucking is apparently an opeiation purely mechanical. The 

 teat is seized, and so closely compressed by the lips of the foal, 

 that the imbibing effort which follows has a tendency to pro- 

 duce a vacuum in the lactiferous tubes, now rendered straight 

 from extension : this is counteracted by the pressure of the at- 

 mosphere upon the surface of the udder, and the consequence is, 

 that the milk is forced from its reservoirs into the mouth, on the 

 same principle that water is impelled into the barrel of a syringe 

 by raising the piston. 



