NERVES OF THYROID AND PARATHYROID BODIES 93 



in thick xylol-balsam. The slides should then be warmed until 

 enough of the xylol has evaporated to leave the balsam brittle 

 on cooling, and while still warm, covered by warmed cover slips. 

 Preparations prepared in this way are permanent. 



THE NERVES OF THE THYROID 



The nerves which go to the thyroid are entirely of the non- 

 medullated variety and reach it from the neighboring cervical 

 sympathetic ganglia by following the perivascular connective 

 tissue and the tunica adventitia of the thyroid arteries. It is 

 often very difficult to examine these nerves, for they are obscured 

 in sections stained by the chrome silver method by large amounts 

 of black and brown precipitates, and by the staining of the fat. 

 By carefully examining sections where there is only a small amount 

 of fat, or better, by studying sections stained by the methylene 

 blue method, the nerves accompanying the blood vessels can be 

 followed. They appear as large, wavy, irregular strands, com- 

 posed of individual varicosed axis-cylinders collected together 

 into bundles similar to the wires in a cable. 



These nerves do not branch elaborately outside the gland; the 

 only branches coming from them are small ones which form the 

 perivascular plexuses in the arterial walls, and probably furnish 

 the vaso-motor supply. As soon as the arteries penetrate into 

 the gland substance they branch profusely, this branching being 

 accompanied by a corresponding branching of the nerves, so that 

 as the arteries decrease in size there is a similar decrease in the 

 size of the accompanying nerves. The nerves supplying these 

 smaller arteries (fig. 2) form an elaborate perivascular plexus, and 

 give off the branches which penetrate between the follicles, and 

 form the perifollicular plexuses. The latter are the only ones 

 that can be said to be the true glandular or secretory nerves. 



The arterial or perivascular plexuses are formed by the branches 

 of a few relatively large nerve trunks (fig. 2, A), lying in the con- 

 nective tissue immediately surrounding the vessels, and having 

 a course parallel to that of the arteries. The branching from these 

 nerves is very irregular; the branches taking any direction after 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 13, NO. 2 



