| third tonsil | A collection of more or less closely aggregated lymphoid nodules on the posterior wall and roof of the nasopharynx, the hypertrophy of which constitutes the morbid condition called adenoids. Synonym: tonsilla pharyngealis, tonsilla adenoidea, Luschka's gland, Luschka's tonsil, third tonsil. (05 Mar 2000) |
|---|---|
| third trochanter | An occasional process at the proximal end of the lateral lip of the linea aspera of the femur, about on a level with the lesser trochanter, giving insertion to the greater part of the gluteus maximus muscle. See: gluteal tuberosity. (05 Mar 2000) |
| third ventricle | A narrow, vertically oriented, irregularly quadrilateral cavity in the midplane, extending from the lamina terminalis to the rostral opening of the mesencephalic aqueduct. This ventricle communicates at its rostrodorsal corner with each of the two lateral ventricles through the left and right interventricular foramen of Monro. Its narrow roof is formed by the tela choroidea which is attached on either side to the tenia thalami; its lateral wall by the medial surface of the thalamus and, below the hypothalamic sulcus, by the hypothalamus which also forms its floor. In lateral profile, the third ventricle exhibits a number of recesses: in its floor, from before backward, 1) the preoptic recess in the acute angle between the base of the lamina terminalis and the dorsum of the optic chiasm, 2) the infundibular recess extending ventrally into the infundibulum but (in humans) not into the hypophysial stalk, and 3) the mamillary or inframamillary recess caused by the protrusion of the mamillary bodies into the ventricle. From its dorsocaudal corner, the pineal recess extends caudally into the pineal stalk. Synonym: ventriculus tertius, diacele, ventricle of diencephalon. (05 Mar 2000) |
| third ventriculostomy | An operation to establish an opening from the third ventricle to the prechiasmal and interpeduncular cisterns (Stookey-Scarff operation) or from the third ventricle to the interpeduncular cistern (Dandy operation). (05 Mar 2000) |