PATHOLOGICAL ANATOMY AND HISTOLOGY 561 



roids are not as common in man as in lower animals. They are not un- 

 common in the rat (Erdheim), Togofuku having found in one instance 

 as many as eleven. In man more than four glands are reported by Zucker- 

 kandl, Chantemesse, Marie, Miiller, Erdheim and others; more often a 

 smaller numher is reported. In a series of forty autopsies, in which a 

 careful search for the parathyroids was made, Thompson found four gland- 

 ules in thirty-three cases, three of which showed accessory parathyroids, 

 three glands in four cases, two parathyroids in two cases, and an absence 

 of parathyroids in one case. In none of the cases of this series were there 

 any manifestations which could be attributed to the abnormal number of 

 parathyroids. In one instance, MacCallum found five pairs of parathy- 

 roids in a case of gastric tetany. In a further series of sixty-four autop- 

 sies, he found four glands in thirty-six of these, three in ten, two in fif- 

 teen, and one in three. Petersen at times was able to find only one parathy- 

 roid, and in other cases two or three glandules, variously distributed at 

 the poles of the thyroid. Erdheim in one instance found as many as eight. 

 Kogers and Ferguson reported the complete absence of parathyroids in 

 twelve cases out of fifty-four bodies examined. In the latter cases it is 

 probable that these small structures were overlooked. 



Variations in Number in Fetuses and Infants. In case of the human 

 fetus, or newborn infant, as in very young animals, it is difficult at times 

 to differentiate the parathyroids because of the presence of small projec- 

 tions of thyroid tissue which not yet possessing a colloid secretion and a 

 mature morphology may resemble very closely parathyroid tissue. Yere- 

 bely found fewer than four parathyroids in six per cent of the cases studied 

 (138). He never observed more than four. The usual size was 2 to 19 

 mm. long, 2 to 9 mm. broad and 1 to 4 mm. thick. Yerebely states that 

 small portions of the parathyroid may appear in the thyroid or thymus, 

 and also that small islands of thymus tissue containing HassalFs cor- 

 puscles may be present in the normal parathyroids. 



Variations in Number in Animals, The inconstancy in number of 

 parathyroids is still greater in lower animals than in man. Observations 

 have been made with particular reference to the dog, in which it was not 

 uncommon to find supernumerary structures. Gley and Leighton found 

 as many as eight, while in one instance we isolated as many as twelve in an 

 adult dog. The supernumerary parathyroids may be distributed about the 

 thyroid lying externally to its capsule, and usually upon the posterior and 

 lateral borders, but they may also appear buried in the substance of the 

 thyroid or at times at some little distance from the lower pole. It is 

 more common to find the accessory parathyroids, towards and beyond the 

 lower pole of the thyroid than at the upper poles or above this level. In the 

 majority of instances it is necessary to confirm the macroscopic finding of 

 the small glandule by microscopic study. Small islands of pinkish gray 

 lymphatic tissue may be confused with true parathyroid tissue. 



