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E. V. COWDRY 



inferior thyroid veins and esophagus, and may be placed in the thorax 

 near to, or embedded in, the thymus. They have even been recorded as 

 far caudad as the areolar tissue about the pericardium. 



Both glands usually occur in association with the inferior thyroid 

 arteries, which constitute the best clews to their location. 



Blood Supply. Each gland is supplied by a special branch from the 

 inferior thyroid artery, which, after penetrating the capsule, breaks up 

 into numerous branches, which ramify in the connective tissue framework 



Fig. 2. Diagram of median sagittal section of a human embryo showing position 

 of gill clefts, after Bailey and Miller, modified. 



of the organ. The blood is returned through the capillaries into a venous 

 plexus on the surface of the gland, which communicates, in turn, with the 

 thyroid veins. Detailed accounts of variations in blood supply are given 

 by Kohn (/;), by Halsted and Evans, and by Pool and Ealk. 



Lymphatics. The lymphatics have not been studied in detail, but it 

 is clear that they are intimately associated with those of the thyroid gland, 

 the lymph of the two glands intermingling. 



Innervation. The nerve supply from the perivascular sympathetic 

 plexuses is very scanty and apparently escaped observation until the recent 

 work of Rhinehardt. The exact mode of termination of the fibers is not 

 definitely known; some of them, however, are certainly vasomotor in 

 nature. Fibers ending on and between the gland cells have been recorded. 

 As contrasted with the thyroid, the innervation is relatively scanty. 



