762 THE THYROID BODY. [BOOK n. 



into veins also relatively large, which forming plexuses on the 

 surface of the organ end in the superior middle and inferior 

 thyroid veins. The thyroid body is thus furnished with an abun- 

 dant supply of blood. 



The septa also contain a very large number of lymphatic vessels. 

 which, both on the surface of the organ and along the septa, are 

 arranged in plexuses of anastomosing trunks of considerable size. 

 Small nodules of adenoid tissue are also found in the septa. 



The nerves of the thyroid body are also abundant. They are, 

 in man, derived chiefly from the cervical sympathetic nerve, 

 passing oft' from the middle and lower cervical ganglia ; their 

 exact terminations within the organ is not known. Fine filaments 

 are also said to be given off to it from the external branch of the 

 superior laryngeal nerve. 



The 'accessory' thyroid bodies often found are of the same 

 nature as the main body. 



Very frequently, so frequently in the adult as to be of almost 

 normal occurrence, the alveoli contain not simple glairy fluid 

 but a more solid clear material, called 'colloid'; this generally 

 appears in the centre of an alveolus and may fill up the whole 

 lumen ; occasionally more or less changed epithelial cells may be 

 seen lying between it and the layer of cells resting on the base- 

 ment membrane. Extravasations of blood into the alveoli are also 

 not uncommon. 



The thyroid body is very apt to become enlarged, sometimes 

 enormously so ; and is then spoken of as goitre. The enlargement 

 may be due simply to an increase in the number of otherwise 

 fairly normal alveoli and septa. But very often a number of 

 alveoli become more or less confluent, forming a cyst ; and at times 

 the whole gland appears to be composed of a number of cysts of 

 varying size, frequently loaded with ' colloid ' material. There is 

 also a form of goitre in which the enlargement is chiefly or even 

 exclusively due to an increase in the vascular supply, the blood 

 vessels being abnormally distended; and this apparently may 

 occur without any structural changes in the walls of the blood 

 vessels. Sometimes however the arteries undergo aneurismal 

 enlargements, with changes in their coats. 



The glairiness of the fluid contents of the alveoli has generally 

 been attributed to the presence of mucin, and this body has also 

 been said to have been found within the lymphatic vessels running 

 in the septa ; but some observers have urged that the material in 

 question is not true mucin, but a peculiar form (or forms) of 

 proteid substance. The * colloid ' material so frequently appearing 

 has also been regarded as allied to mucin, but its exact nature has 

 not as yet been satisfactorily determined. Besides these special 

 substances the alveoli or cysts also contain serum-albumin and 

 globulin. The 'extractives' of the thyroid appear to contain 

 kreatin or kreatinin in not inconsiderable quantities, xanthin, and 



