CHAPTER V.
DISEASES OF THE MAMMARY GLANDS.
In animals used for the purpose of providing milk, viz., cows, goats, and milch ewes, diseases of the mammary glands are of daily occurrence, but are rare in those in which the mammary function is limited to the nourishment of the young, such as the mare, female ass, sow, etc.
In order clearly to understand the development of these diseases, it is necessary to bear in mind the anatomical construction of the organs, for which purpose we may take as a type the mammary gland of the cow, which is the most complicated.
The udder of the cow is of hemispherical shape. It is situated in the inguinal region, and is composed of two parts, the right and left, which are absolutely independent and can easily be isolated from each other along the median plane throughout their extent. The mass of parenchyma is enveloped in a fibrous envelope, which is covered with a very loose layer of subcutaneous connective tissue. Each half is subdivided into two quarters, an anterior and a posterior quarter. Each quarter again represents a distinct gland, although anatomical separation between the anterior and the corresponding posterior quarter would be almost impossible, the separating fibro-connective partition being common to both glands.
In very good milkers it sometimes happens that two small supplementary glands may be found behind the posterior quarters, bringing up the total number to six.
Parenchyma.—Each of these glands is provided with a teat containing a large sinus. Anatomically the mamma consists of glandular tissue arranged like a bunch of grapes, in which the active tissues of the acini deliver their secretion into little excretory canals, which unite, forming a large collecting plexus. The collecting canals, or galactophorous canals, open into the galactophorous sinus, which occupies the entire depth of the teat and communicates with the exterior by a small pore provided with a sphincter. The interacinous connective tissue of the udder and the subcutaneous tissue of the teat, which envelops the galactophorous sinus, is extremely rich in elastic fibres, enabling the organ to undergo great changes in volume without injury.
Vessels.—The mammæ are supplied by two great arteries, the mammary arteries, which are given off from the prepubic arteries, pass into the inguinal canal, and penetrate the gland by its upper, deep face. Each principal lateral artery divides into two trunks, one for the anterior, the other for the posterior quarter.
Fig. 237.—Schema showing the structure and organisation of the udder. Antero-posterior section showing the arrangement of the anterior and posterior quarters and the teats, skin, transverse partition, etc. GRM, Retro-mammary lymph gland; Lp. lymphatics of the posterior quarter; La, lymphatics of the anterior quarter; LE, efferent lymphatics; AM, mammary artery; VM, mammary vein; VMa, anterior mammary vein (subcutaneous abdominal vein); C, transverse intermammary septum.
The veins which collect the blood from the mammæ form two systems, the first accompanying the mammary arteries, the second, more superficial, giving rise to the anterior subabdominal mammary veins. The arterio-venous plexus of the udder, which represents the vascular pedicle of the organ, penetrates the gland, near a line dividing the posterior and middle thirds of the upper surface, an inch or so in front of the mammary lymphatic gland.