172 JEEEMIAH S. FERGUSON 



a fine needle directly into the thyroid sinus may force the fluid into 

 either the venous or the lymphatic plexus, according as the one or 

 the other sj'^stemof vessels happens to be entered. I am convinced, 

 as a result, of my injection experiments, that the lymphatics open 

 freely into the veins of this part, after the manner of the '' vasa lym- 

 phatica" of Favaro {vide infra). These observations are of interest 

 in connection with Baber's inability to find lymphatics in the thy- 

 roid gland as indicating the relation between the vascular systems. 

 I find, however, that it is not possible for fluids injected into the 

 thyroid sinus or its plexus of lymphatics to pass in any quantity 

 into the vessels within the thyroid gland; this is presumably 

 because of the presence of valves. 



The alternate expansion and contraction of the mouth and phar- 

 ynx, forcing the stream of water through the branchial clefts, 

 alternately fills and empties the thyroid sinus, so that by means of 

 these respiratory movements the sinus acts somewhat after the 

 manner of a venous heart. In this connection it is interesting 

 to consider the observation of Favaro ('06), as quoted by Sabin 

 ('09), that the relation of the veins and lymphatics in fishes is 

 much more primitive than in mammals and that both lymph- 

 hearts and vein-hearts may be present in these animals. The 

 emptying and filling of the veins can readily be seen in the Selachii 

 or Raia on removing the skin, or even through the integument in 

 the living skate, the colored blood showing readily through the 

 vascular walls. The relation of the lymphatics to the blood-sinus 

 is so intimate that they must also be emptied and filled in the same 

 way, though since they contain a colorless fluid they can not be so 

 readily observed. I have, however, demonstrated that a colored 

 fluid injected into these lymphatic vessels will overspread the 

 thyroid region in ten to fifteen minutes and will almost entirely 

 disappear within the next fifteen minutes ; the lymphatic circu- 

 lation must therefore proceed with considerable rapidity. 



The thyroid artery approaches the organ from either side; in 

 Mustelus and Squalus it enters at the extreme lateral angle of the 

 triangular gland (fig. 19). In Raia, where the organ is of a more 

 rounded form it enters near the middle of the lateral border. The 

 branches of the artery ramify upon the surface of the organ send- 



