INTERNAL STRUCTURE OF COW'S UDDER 25 



of this opening, or at the end of the teat, there is a sphincter 

 muscle, which in some cases is drawn up very tight, while in 

 other instances it is so loose that it will not prevent the milk from 

 escaping. In case the muscle is so tight that the milk can be 

 drawn only with difficulty, it may be relaxed a trifle by inserting 

 a small, smooth wooden plug. This will usually dilate the open- 

 ing sufficiently, so that the milk may be drawn with comparative 

 ease. In some instances this muscle is so tight that it is necessary 

 to relax it by the use of a sharp knife. This, however, should be 

 done with surgical skill; otherwise the whole muscle is likely to be 

 so injured as to cause the milk to leak away at all times. 



The upper part of this canal in the teat connects with what 

 is called the milk-reservoir. The size of this reservoir varies in 

 different cows. The average capacity of this milk-cistern is 

 about one pint. The opening from this reservoir into the teat 

 is also guarded with a muscle. Over this muscle the cow has 

 little control; over the muscle at the lower end of the teat she 

 has no control whatever. 



Opening into the sides and top of this reservoir are a large 

 number of tubes, which are called milk-ducts. These milk-ducts 

 extend from the reservoir up into the milk-gland. They radiate 

 in all directions, divide and subdivide, so as to form a very large 

 number of small tubes. These milk-ducts are surrounded with 

 fibrous muscular tissue, nerves, and blood-vessels. They are all 

 guarded by a special muscle at the junction with the main milk- 

 ducts, from which they radiate. These muscles are so inti- 

 mately connected with the nerves and muscular system of the 

 cow that she is able to open and close them at will. There are 

 very few cows that are not able to hold up their milk during 

 nervous and exciting periods. It is a common occurrence for a 

 milker to get only a small part of the milk from a cow ; this small 

 amount is the portion which is present in the teat and milk- 

 reservoir. Some cows are able to hold up this milk also, but the 

 majority of cows cannot perfectly control the muscle which 

 guards the entrance to the teat. The milk which is present in 

 the milk-ducts and which has to pass through these junctions 

 referred to above can be held up by most cows at will. 



