before a vowel trit-, combining form repr. Gr. τρίτος third, occurring in several technical, mostly scientific, terms (usually corresponding to terms in PROTO-, and DEUTERO- or DEUTO-). 1. Generally.
ǁ Tritencephalon [mod.L., f. Gr. ἐγκέφαλος brain], the third of the three primary cerebral vesicles of the embryo; also, the hindmost segment of the brain of an insect. Tritocere [Gr. κέρας horn], that tine of a deer’s antler which is third in order of development (Cent. Dict., 1891). ǁ Tritocerebrum, erron. -on [mod.L., f. L. cerebrum brain], = tritencephalon; hence Tritocerebral a., pertaining to or constituting a tritocerebrum. Tritocone, the posterior external cusp of a premolar tooth. Trito-Isaiah [after DEUTERO-Isaiah], a later author to whom a third section of the book of Isaiah is attributed by some critics. Tritomesal a. [Gr. μέσος middle], applied to a series of cells in the wings of hymenopterous insects, now usually called the submedian second discoidal and first apical cells. Tritotoxin: see quot. 1904 s.v. prototoxin (PROTO- 2 b). Tritovertebra, in Carus’s nomenclature (1828), applied to the bones of the limbs reckoned as the third set of vertebræ; hence Tritovertebral a., pertaining to or of the nature of a tritovertebra. Tritovum, a third stage of an ovum, succeeding the deutovum. Tritozooid, a tertiary zooid, produced from a deuterozooid.
1910. Encycl. Brit., XIII. 425/2. This anterior or ‘brain’ mass consists of three lobes (the prot-, deut-, and *tritencephalon of Viallanes). Ibid., 418/2. An ‘intercalary’ or *tritocerebral segment has been demonstrated … in various insect embryos.
1898. Packard, Text-bk. Entom., 231. Viallanes first … divided the brain of adult insects into three regions or segments; i. e. the ‘protocerebron,’ ‘deutocerebron,’ and *‘tritocerebron.’ Ibid., 237. The œsophageal lobes (Tritocerebrum).
1896. Proc. Zool. Soc., 5 May, 563 (Premolars). The antero-external cusp (protocone of Scott) … develops first, the antero-internal or deuterocone second, and the tetartocone third, the *tritocone being wanting.
1908. Athenæum, 7 Nov., 565/2. A *Trito-Isaiah besides a Deutero-Isaiah.
1826. Kirby & Sp., Entomol., III. xxxv. 632. The medial areolets … form three distinct series; these may be called the protomesal, deuteromesal, and *tritomesal.
c. 1860. S. Kneeland, Jr., in Amer. Cycl., XIII. 424 (Cent. Dict.). [Carus] makes what he calls proto-, deuto-, and *trito-vertebræ.
1902. Cassell’s Encycl. Dict., Supp., *Tritovertebral.
1877. Huxley, Anat. Inv. Anim., vii. 385. In the Acarus of the Mouse, Claparède observed that the deutovum stage is followed by a *tritovum.
1861. J. R. Greene, Man. Anim. Kingd., Cœlent., 74. The medusoids budded by Sarsia are, probably, *tritozoöids.
† 2. In Chemistry, formerly used, after T. Thomson (Syst. Chem. [1804], I. 103), in naming the third oxide, sulphuret, iodide, etc., in a series in ascending order (cf. PROTO- 3 a, DEUTO- 1). Obs.
1806–50. [see TRITOXIDE].
1825. T. Thomson, First Princ. Chem., II. 481. Tritosulphuret of potassium.
