Lymphatics.—On either side of the middle line lies an extremely rich lymphatic plexus, the origin of which is to be found near the ends of the teats and in the peri-acinous spaces.
The superficial collecting vessels are dispersed under the skin, perforate the fibrous sheath towards the base of the teat, and anastomose with one another on the surface of the gland, the anastomosis being most intimate between those of the same quarter, finally emptying separately by two large trunks into the retro-mammary lymphatic gland of the same side.
The vessels of the anterior quarter enter the lymphatic gland at its most anterior point; those of the posterior quarter join it a little below.
The retro-mammary lymphatic glands are two in number, and are situated very high and towards the back, above the posterior quarters and close to the perineum, outside the fibrous envelope of the gland. They are sheltered in a recess excavated within the depths of the gland itself. The main collecting lymphatics from the anterior and posterior quarters enter it separately.
The lateral efferent vessels are divided into two groups, one of which ascends vertically in the perineal region, towards the lymphatic glands round the anus; the other passes through the inguinal canal towards the sublumbar region, together with the blood-vessels.
The mammary nerves are two in number. The anterior has a downward course outside the fibrous envelope and supplies the teat; the posterior nerve is similarly distributed. In other domestic female animals which have only two mammæ the general arrangement is precisely the same.
PHYSIOLOGICAL ANOMALIES.
Imperforate condition of the Teat.—It sometimes happens that although the udder is otherwise well formed, the teats, or more frequently a single teat, proves to be imperforate. Between the galactophorous sinus and the exterior, opposite the sphincter, a little membrane may be found which closes the teat and entirely prevents the contents of the udder from escaping. Its existence is only discovered when the animal first calves and lactation commences. Not a drop of milk can be withdrawn, although the udder is swollen. Local examination readily reveals the defect.
Treatment is very simple and effective, the membrane being perforated with the end of a milk catheter.
Contraction of the Sphincter (Atresia of the Extremity of the Teat).—Under other circumstances the teat may present a distinct perforation, and yet milking may be impossible, or at all events may be extremely difficult. This is sometimes due to contraction of the sphincter, or possibly to atresia of the orifice.