Sweat glands are infrequent in dermoids. Teeth are quite common. These may vary in number from two or three up to several hundred—may be embedded in definite sockets or simply sprout from the cyst wall. Occasionally bone material, lodging such teeth and crudely resembling a jaw, will be found.

Dermoids containing mucous membrane are found, especially in connection with the ovary and with the postanal gut (i. e., the original communication between the spinal and alimentary canals).

It is curious that under these circumstances mucous membrane is sometimes furnished with hair, as it normally is in the stomach or other cavities of some of the lower animals. Mucous glands and retention cysts of these glands are also found in ovarian dermoids. This will be more readily understood if the mutability of skin and mucous membrane be not forgotten. The transition from one to the other is not difficult, and we find all intermediate stages between the two extremes—if not in man, at least in animals. This will account for the fact that skin-covered dermoid tumors are found in certain parts of the alimentary canal, and particularly in the pharynx. These tumors grow also from the mucous membrane of the bowel, of the rectum, or even of the small intestine.

Sutton has made a division of dermoids into three classes:

1. Sequestration Dermoids.

—Sequestration dermoids occur chiefly in situations where during embryonic life coalescence takes place between two surfaces possessing an epiblastic covering, although sometimes this coalescence practically occurs late in life and by implantation.

Dermoids of the trunk occur particularly where opposite halves of the body wall coalesce—that is, in the midline of the trunk and head. Dermoid cysts are rarely found in connection with spina bifida, and certain tumors spoken of as spina bifida undoubtedly are dermoids. Anteriorly dermoids occur frequently in the scrotum, and occasionally in the testicle. At the umbilicus they are rarely found—usually as pedunculated tumors projecting externally. In the midline of the thorax and neck they are most common opposite the manubrium, dropping down behind it to invade the anterior mediastinum. Near the hyoid bone they occur relatively frequently; about the head they are met with most commonly at the angles of the orbits—more so at the outer than at the inner angle. Dermoid cysts are known to oculists as growing upon the iris or springing from the conjunctiva. About the ear they are not infrequent; in the roof of the mouth, especially if this be incomplete, we frequently find cysts of epiblastic origin.

Sequestration dermoid cysts are also undoubtedly found in connection with the dura mater, in the scalp, most commonly at the anterior fontanelle, at the root of the nose, and at the external occipital protuberance, where they may be confounded with sebaceous cysts or with meningoceles. In order that a dermoid of the dura may communicate with the skin there must of course be osseous defect.

Sequestration dermoids upon the limbs have been mostly reported as sebaceous cysts. They are rare, and usually associated with antecedent injury, by which epiblastic structures are driven in and implanted in such a way that as they develop they give rise to these peculiar tumors. These are what Sutton calls implantation dermoids. They are found upon the fingers and elsewhere.