266 ANATOMY AND PHYSIOLOGY 



ing as, normally, it should do; if it is fixed by adhesions or by excessive 

 growth it exerts traction upon the larynx and trachea which is visible during 

 the movements of swallowing. 



The function of the thyroid body is important but not well 

 explained. It is observed that the development of both mind and 

 body is arrested if the thyroid be absent, or if it does not itself 

 develop in childhood; this condition is known as cretinism. 



Degeneration or complete removal, in adult life, is followed by 

 excessive growth (but imperfect development) of connective tissue 

 and skin elements, or myxedema, and a gradual deterioration of 

 mental power. These effects may be prevented by leaving a 

 small portion of the gland in place or by transplanting it. 

 . From these and other clinical observations it is evident that 

 the internal secretion of this body exercises an important influence 

 upon nutrition. It stimulates cardiac action, increases blood 

 pressure, and restrains a tendency to obesity. 



Clinical notes. Simple enlargement of the thyroid body constitutes 

 goiter, which is said to be frequent in certain countries where the drinking 

 water contains much lime. 



Exophthalmic goiter is a diseased condition of the thyroid body with the 

 following symptoms: Enlargement and pulsation of the thyroid, rapid heart 

 action, tremor, and protrusion of the eyeballs. 



THE PARATHYROID BODIES 



The parathyroid bodies are small bodies situated above and 

 laterally to the thyroid, two on each side. They have an abundant 

 blood supply. Their function is not explained but it is now known 

 that their removal is soon followed by convulsive affections, 

 tremor, etc., suggesting the presence of an irritant in the blood 

 which did not exist before. Consequently it may be that their 

 internal secretion is able to neutralize certain toxic substances 

 formed elsewhere, and capable of causing death. 



Both parathyroid and thyroid bodies contain iodin in combina- 

 tion with some other substance. 



THE THYMUS BODY 



The thymus body (Fig. 171) is an organ of fetal and infantile 

 life, situated below the thyroid, being mostly in the thorax and ex- 



