Lymph glands are, for the most part, arranged in groups or chains, such as those in the axilla, neck, and groin.  In any given situation they vary in number and size in different individuals, and fresh glands may be formed on comparatively slight stimulus, and disappear when the stimulus is withdrawn.  The best-known example of this is the increase in the number of glands in the axilla which takes place during lactation; when this function ceases, many of the glands become involuted and are transformed into fat, and in the event of a subsequent lactation they are again developed.  After glands have been removed by operation, new ones may be formed.

The following are the more important groups of glands, and the areas drained by them in the head and neck and in the extremities.

#Head and Neck.#—­The anterior auricular (parotid and pre-auricular) glands lie beneath the parotid fascia in front of the ear, and some are partly embedded in the substance of the parotid gland; they drain the parts about the temple, cheek, eyelids, and auricle, and are frequently the seat of tuberculous disease. The occipital gland, situated over the origin of the trapezius from the superior curved line, drains the top and back of the head; it is rarely infected. The posterior auricular (mastoid) glands lie over the mastoid process, and drain the side of the head and auricle.  These three groups pour their lymph into the superficial cervical glands. The submaxillary—­two to six in number—­lie along the lower order of the mandible from the symphysis to the angle, the posterior ones (paramandibular) being closely connected with the submaxillary salivary gland.  They receive lymph from the face, lips, floor of the mouth, gums, teeth, anterior part of tongue, and the alae nasi, and from the pre-auricular glands.  The lymph passes from them into the deeper cervical glands.  They are frequently infected with tubercle, with epithelioma which has spread to them from the mouth, and also with pyogenic organisms. The submental glands lie in or close to the median line between the anterior bellies of the digastric muscles, and receive lymph from the lips.  It is rare for them to be the seat of tubercle, but in epithelioma of the lower lip and floor of the mouth they are infected at an early stage of the disease. The supra-hyoid gland lies a little farther back, immediately above the hyoid bone, and receives lymph from the tongue. The superficial cervical (external jugular) glands, when present, lie along the external jugular vein, and receives lymph from the occipital and auricular glands and from the auricle. The sterno-mastoid glands—­glandulae concatinatae—­form a chain along the posterior edge of the sterno-mastoid muscle, some of them lying beneath the muscle.  They are commonly enlarged in secondary syphilis. The superior deep cervical (internal jugular) glands—­from six to twenty in number—­form a continuous