THE MAMMARY GLANDS
In sows the ventral contour of the abdomen is made irregular by the presence of the mammary glands, of which there are almost invariably seven pairs arranged in a double row extending from the thorax to the groin (Figure 34-1; see also Figure 33-1).
Each gland is pendulous and, though confluent with its neighbors at its base, is otherwise clearly defined. Those at the caudal end of the series are generally the largest, but the cranial ones are the most productive.The teats are elongated and cylindrical; each has two openings at its tip (Figure 10-31, B) leading to independent gland units. Some teats tend to project a little to the side, and because sows generally suckle while laterally recumbent, certain teats may not be readily accessible to the litter; some glands may therefore be little used and regress early. On the other hand, when the litter is large some piglets may find it hard to obtain an adequate share of milk and may fail to grow normally.
The blood supply is provided by local vessels: the internal thoracic and the cranial and caudal superficial epigastric arteries. The venous drainage is satellite. Lymph from the first two (or three) pairs of glands leads to ventral superficial cervical nodes, and that from the remainder leads to the superficial inguinal.