Edentata: │ │ │ Anteater │ 3,300│ 2.│ .6 Myrmecophaga tetradactyla│ │ │ Accipitres: │ │ │ Wedgetailed Eagle │ 2,300│ 1.│ .43 Aquila audax │ │ │ Struthiones: │ │ │ Rhea │ 18,000│ 5.│ .27 Rhea americana │ │ │ Emu │ 36,300│ 23.│ .63 Dromæus novæ-hollandiæ │ │ │ ─────────────────────────────┴─────────────┴─────────────┴───────────── ANATOMY. The minute anatomy of the normal thyroid is fully given in text-books, and is doubtless pictured in the minds of all but students of the subject as a fixed and definite affair. Such is not the case. There is certainly a variation in gross size under conditions of seasonal and sexual activity, and it would seem acceptably demonstrated that changes in diet, especially where meat is concerned, are associated with swellings or shrinkage of the glands. These gross changes must be due to alterations in histology. In youth also the bulk is larger, a condition due to cellular activity, while as middle age advances the thyroid becomes smaller and more balanced in its colloid and cellular proportions. I need not detail the ultimate constituents of the gland, but it is well to emphasize a few points which must be taken into consideration in microscopical diagnosis. In the first place, the lobules or acini are not all of the same size in normal organs. This is especially true in the normal adult gland but may be so in youth. The cells which form the inner lining of the acinus are low cuboidal in shape but the elements which lie under them are oval and do not change with hyperplasia of the former. The colloid which fills the glandular spaces is very susceptible to mechanical and chemical agencies. In material preserved in alcohol it may be shrunken away from the cells or heavily vacuolated, while in tissue preserved a long while in any liquid it may be found contracted or broken. Large vacuolated or vesicular cells are characteristic of the human parathyroid; this type is by no means so prominent in the lower animals, and in the few examples studied closely the arrangement is less definitely glandular than in man. The avian thyroid is distinct from the mammalian in the delicacy of its fibrous framework and the flatter character of its epithelia. Acini are usually of more uniform size. Capsular vessels are prominent but internal vascularity is less in birds than in mammals and their goitres are not solid. PHYSIOLOGY.