The tonsil is composed of lymphoid tissue, and is situated between the pillars of the fauces, being kept in position by fibrous bands, which connect its deep surface with the muscles of the palatine arches. This deep surface is closely in relation to the superior constrictor of the pharynx, but is not as near the external carotid artery, which lies in loose, fatty tissue about an inch behind, and considerably external to the tonsil. Thus there is practically no possibility of wounding the carotid in the operation of tonsillotomy, save where, in old age, the vessel has become very tortuous. The facial or ascending pharyngeal arteries or glossopharyngeal nerve are in greater danger of being wounded. The inner or free surface is convex, and presents numerous depressions corresponding to the orifices of the crypts. A small depression at the upper extremity is known as the supratonsillar fossa, and is said to represent the pharyngeal extremity of the second branchial cleft. The blood-supply is abundant, being derived from branches of the facial, ascending pharyngeal of the external carotid, descending palatine branches of the internal maxillary and small branches of the dorsalis linguae. The veins form a plexus on the deep surface, and communicate with the pharyngeal veins. The lymphatics communicate with the deep cervical glands which overlie the large vessels behind the angle of the lower jaw. The tonsil varies considerably in sizte within normal limits, and in tonsillitis or cynanche tonsillaris may become very much enlarged, the two tonsils meeting in the middle line, and leaving a very small breathing space, while swallowing becomes very difficult. Where the enlargement becomes chronic, tonsillotomy has frequentfy to be performed. Deafness is frequently complained of in cases of enlarged tonsils, being due, probably, to accompanying hypertrophy of the lining membrane of the Eustachian tube rather than to direct pressure. Decomposition of secretions retained in the crypts frequently occurs, giving rise to foetid breath, and calculi may form, and give rise, through irritation of the glosso-pharyngeal nerve, to a spasmodic cough. Tonsillar abscesses, which not infrequently complicate scarlet fever, occur interstitially or between the tonsil and the pharyngeal wall. Movements of the jaw are interfered with, and the glands at the angle of the jaw enlarge. Such abscesses may perforate the pharyngeal wall, and assume a large size, the greatest danger being septic periarteritis of the internal carotid, with consequent bursting and fatal haemorrhage. In opening such abscesses the edge of the bistoury should be turned toward the uvula, the incision being made from without inwards toward the middle line. Lymphosarcoma sometimes occurs in the tonsil de novo. Carcinoma is generally secondary, and rapid involvement of the glands of the neck generally follows. Such cases may be treated through an oblique incision in front of the sterno-mastoid, which enables one to deal with primary disease and affected glands.