URINARY ORGANS AND MAMMARY GLANDS. 57 



Coats. — Three: mucous, muscular (of several layers), and 

 serous (peritoneal). 



Urethra. — This is the canal which conducts urine from blad- 

 der to exterior of body. 



MAMMARY GLANDS. 



The cow's udder is taken as a type. The glands are lo- 

 cated under the inguinal region and supported by skin, loose 

 connective tissue and bands of white fibrous tissue which at- 

 tach to the fibrous tunic of the abdomen and act as ligaments to 

 help support the organ. The udder is covered by thin, soft 

 skin and fine hair. 



Anatomy. — The udder is divided into two lateral halves. 

 Each half has two glands, front and back, and each half is en- 

 cased in a fibrous sac of yellow elastic tissue. 



The substance of each gland is made up of yellow gland- 

 ular tissue, connective tissue, nerves, blood vessels, etc. Each 

 gland is divided into lobes, and these again into lobules. 



There is one small milk duct for each lobule. These unite 

 into larger and larger ducts, and thus the milk is conveyed into 

 the milk cistern. 



A milk cistern is located just above the base of each teat. 

 This receives milk from the milk ducts — capacity one pint to one 

 quart. Milk escapes from cistern through a single large canal. 



Development. — The gland structure is undeveloped and ru- 

 dimentary until maturity, and only becomes active at the close 

 of the first pregnancy. 



Function. — Natural function is supplying sufficient milk to 

 the calf until it can subsist on other foods. 



Milk production. — The production of the casein, sugar, fat, 

 etc., is a manufacturing process, not mere filtration for there is 

 no casein or milk sugar in blood and but very little fat. Secret- 

 ing cells take certain elements from the blood and put them to- 

 gether so as to make the milk ingredients. 



Products. — Milk is a complex alkaline fluid; specific grav- 

 ity 1018 to 1040, composed of oil globules suspended in milk 

 plasma and is therefore an emulsion. ]\Iilk globules consist al- 

 most entirely of fat, with a thin coating of casein. They are from 

 .0004 to .0012 of an inch in diameter. Alilk plasma consists of 



Vet. Studies— 4. 



