The thyroid gland in its functional capacity, may be considered to undergo hyperplasia and then atrophy of the parenchyma cells. Normally this would leave the colloid, the epithelia and the supporting tissue in proper balance, but in the presence of low grade inflammation or where an abnormally hyperplastic process retrogresses, the connective tissues may exceed their norm, the epithelia may be shed or remain high and the colloid be irregular in distribution. Such a state of atrophy may exist in fetal life, arise from unknown cause during a course of toxic goitre, or perhaps insidiously in chronic toxic conditions. When this occurs in fetal life cretinism or myxedema arises, when in later life, only the latter appears. Judged entirely by microscopic findings, eight instances of atrophic changes in the thyroid have been found. Three of these were in Carnivora and were secondary to definite goitres, but were not followed by myxedema; one of these three was a cretin. A brother of this cretin but not himself a cretin, died at the age of five months from acute dilatation of the heart, and with a decidedly atrophic thyroid gland. A lion showed a distorted gland, the result of chronic inflammation, a condition also present in a leopard, in the latter possibly in association with a general infection of the heart, vessels and kidneys of long standing. A case in a bear can only be explained on the basis of chronic intestinal toxemia. A camel is the only other variety of animal to show this regressive change. The beast suffered with a marked anemia with marrow atrophy and hydatid disease; calcification was found in the thyroid. [Illustration: FIG. 33.—COLLOID GOITRE WITH HEMORRHAGE FROM LEFT GLAND WHICH KILLED THE BIRD. BLACK AREA IS CLOTTED BLOOD. MUTE SWAN (CYGNUS OLOR ♂ ). ] [Illustration: FIG. 34.—AT THE LEFT, THE INSIDE OF THE CALVARIUM SHOWING HEMORRHAGIC PACHYMENINGITIS. AT THE RIGHT IS A FEMUR, SHORT AND HEAVY BUT WITH THIN CORTEX; CONSTRUCTION IS ORDERLY. CRETIN GRAY WOLF PUP (CANIS MEXICANUS). ]