THE PATHOLOGICAL ANATOMY 



271 



relations with the anatomical changes. There are no essential anatom- 

 ical changes in the thyroid that have not their counterpart in other 

 tissues, hence the major groups will be recognized as the accepted group- 

 ings of anatomical changes common to all body tissues. Brooks, Dohrn, 

 Ferguson, Gudernatsch (a,), Hermann and Verdun, His (a), Kastschenko, 

 Kingsbury, Mall, Marine (6)(c) Miiller, A., Miiller, W., (&), Keese, 

 Schneider, Stieda, Stockard. 



The Normal Thyroid 



A definition of the normal thyroid, both gross and microscopic, is obvi- 

 ously the most essential and the most difficult feature of a description of its 

 pathological changes. Since one's conception of the abnormal de- 

 pends upon his conception of the normal, it seems desirable to out- 

 line briefly the salient features of the 

 normal structure as they appear to the 

 author. (See Figs. 5, 6, 7, and 8.) 



All anatomists have recognized the 

 difficulty of defining the limits of normal. 

 This is due to the great range of struc- 

 tural variations dependent upon varia- 

 tions in function. Such variations in 

 structure as are dependent upon season, 

 climate, geographical location, age, sex, 

 food, state of nutrition and many others 

 have not been fully discounted in the 

 published descriptions. Studies in the 

 chemistry must be correlated with the 

 anatomical studies. In our experience a 

 thyroid that has less than 0.1 per cent 

 iodin cannot be normal anatomically, and 

 a thyroid that has continuously had an 

 iodin store above 0.1 per cent cannot be 



abnormal anatomically. The normal human adult thyroid weighs between 

 20 and 25 grams and does not exceed 0.35 gram per kilo, of body weight. 

 The lateral lobes are in 'general symmetrical, the right lobe is usually 

 slightly larger than the left. The isthmus is rarely absent, while the 

 pyramidal portion is highly variable as regards its presence, shape and 

 size. The strictly normal isthmus is a band of thyroid tissue one to two 

 centimeters in width and one-half to one centimeter in thickness connect- 

 ing the lobes in front of the trachea at the level of the third and fourth 

 tracheal rings. The numerous departures from this normal type or the 

 presence of a pyramidal process of variable size, is due to the failure 

 of this portion of the thyroglossal tract to undergo absorption which 

 normally takes place in early fetal life, but which, under the stimulus 



Fig. 5. Normal thyroid of bony 

 fish (Salvelinus fontinalis) com- 

 posed of scattered, rounded alveoli. 

 The relation of the alveoli to bone, 

 cartilage and muscle is shown. 

 (After Marine and Lenhart, J. Ex- 

 per. Med., 1910: 12.) 



