SECTION XI 
THE DUCTLESS GLANDS 
The Thyroid Bodies. 
The ductless glands occupying the anterior cervical 
regions, known as the thyroids and parathyroids are 
structures to be found in some form in all vertebrates, 
but increase in distinctness of outline and construction 
upward in the zoological scale. In the bird they present 
themselves as discrete rounded bodies lying well to the 
side of the midline resting usually upon the carotid artery 
or jugular vein or both. As one removes the skin reddish 
browTi globular masses \viU be exposed to view, sometimes 
showing an irregular lobular outline, a variation due to 
separate but attached masses of parathyroid glandules ; 
the latter may be yellowish or even white. For the most 
part, however, distinct thyroid and parathyroid bodies 
are separated with diflSculty, and one must discover the 
latter by microscopical section. In the mammal these 
organs are by no means so readily found when removing 
the cervical integument, for they are usually buried 
beside the trachea and covered by sternohyoid and 
sternothyroid muscles. Their position, relative to the 
larynx and upper end of the sternum, varies considerably 
but this seems to have little importance in the enlarge- 
ments to which the gland is liable. It is, however, lower, 
that is more posterior, than in the human being, rarely 
rising as high as the lateral thyroid cartilages. The 
principal lobes are elliptical or roughly triangular masses 
with their long axis cori'esponding to that of the 
animal 's body and apposed mesially to the trachea. When 
enlargement occurs it develops in the anterior or ventral 
direction, pushing through the cleft between the muscles 
and the trachea to present under the cervical skin. In 
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