372 THE THYROID GLAND, BY E. VERSON. 



stronger bands which, on the one hand, are connected with the 

 investing sheath, and on the other, isolate large groups of gland 

 vesicles. In this way the thyroid gland of man is divided 

 into primary and secondary segments, the line of division 

 between which is recognisable by slight furrows. In other 

 cases, however, these strong septa may fail, and the whole 

 glandular organ represent a continuous mass. 



The connective tissue lying between the several gland vesicles 

 of the individual segments is very sparing in quantity, and 

 sometimes even it is difficult to discover between the walls of 

 contiguous vesicles a few fibres accompanying the capillaries. 

 Near the investing membrane, and between the peripheral 

 vesicles, it is more abundant. If the fresh vesicles of the tor- 

 toise be isolated by means of needles, we find them invested 

 by a fine network of fibres, which frequently bear branched 

 cells. 



The Arteries are large branches of the thyroid artery, and 

 penetrate into the interior of the gland, following the course 

 of the fibrous septa, dividing the organ into segments or lobules. 

 Their branches accompany the secondary septa, and these 

 again break up into large capillaries having a diameter of 

 0'006 O01 millimeter, that form a network around the 

 several gland vesicles from which again the veins take their 

 origin. These, externally to the fibrous sheath, are character- 

 ised by the width of their lumen and the proportionate thin- 

 ness of their walls. 



The lymphatics, according to Frey, commence with csecal 

 extremities between the gland vesicles, and unite to form 

 meshes surrounding the lobules, finally emerging from the sur- 

 face of the organ as vessels of considerable size. The nerves 

 appear as thick trunks of dark-edged fibres which adhere 

 firmly to the vessels. 



In man the thyroid gland appears to be composed of a me- 

 dian and two lateral lobules united by means of connective 

 tissue. Other mammals, as the dog, calf, horse, etc., possess a 

 thyroid gland consisting of two separated lobules lying on 

 either side of the trachea. 



A single median lobe occurs in Amphibia and Birds, which 

 descends into the thoracic cavity. 



