CHAPTER II 



THE GLANDS: THYROID AND PITUITARY 



The glands of internal secretion, the history of which, as tools 

 of thought, I reviewed in the previous chapter, have each an 

 interesting evolutionary story. Without some acquaintance with 

 that story, the rough outline of their physical architecture, and 

 the particular work they are called upon to perform in the body, 

 no adequate understanding of their influence upon types of 

 human nature and personality is possible. 



The Thyroid Gland 



This gland consists of two maroon colored masses astride the 

 neck, above the windpipe, close to the larynx. These are bridged 

 by a narrow isthmus of the same tissue. They remind one of 

 the flaps of a purse opened up. The gland has always attracted 

 much attention because its enlargement constitutes the prominent 

 deformity known as goitre. 



To begin with, the thyroid was once a sex gland, pure and 

 simple. In the lowest vertebrates and in the homologous tissues 

 of the higher invertebrates, the fractions of the thyroid are inti- 

 mately connected with the ducts of the sexual organs. They 

 are indeed accessory sexual organs, uterine glands, satellites of 

 the sex process. From Petromyzon upward that relationship is 

 lost, the thyroid migrates more and more to the head region, to 

 become the great link between sex and brain. How alive that 

 function still is, is grossly shown by the swelling of the gland 

 with sexual excitement, menstruation and pregnancy. 



Relative to the body weight it is largest in the mammalia, 

 and smallest in the fishes. It therefore grows larger as the 

 f>rate ascends in the scale. It has, in fact, developed in 

 oportion to and side by side with the fundamental, 

 differentiating vertebrate characteristics. Of these, the posses- 

 sion of ;i dry hairy skin instead of a moist or mucus bearing, 

 chitinous skin, the ownership of an internal bony skeleton and 



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