THE ANATOMY OF THE THYROID GLAND 205 



promptly empty into groups of broad interfollicular, blood capil- 

 laries, the venae lymphaticae (figs. 9, 11, 12), which envelop the 

 follicles on all sides. From the venae lymphaticae the veins pass 

 out of the gland at its posterior and lateral borders and dorsal 

 surface to enter the thyroid sinus ; a few veins from the lateral bor- 

 der of the gland pass directly to the hyoid sinus. 



The course of the lymphatics was much .less easily determined 

 than that of the blood vessels. ''Stick injections," as ordinarily 

 made, spread so rapidly through the loose connective tissue of 

 the gland and so easily entered and filled the venae lymphaticae 

 that they entirely obscured the smaller vasa lymphatica. The 

 venae lymphaticae thus injected form a dense almost opaque mass, 

 showing that the thyroid may well occupy the place in these fishes 

 assigned to it by Tscheuwsky ('03) as the most vascular of mam- 

 malian glands. After several futile attempts to inject the lym- 

 phatics in the ordinary way the method was so altered as to inject 

 only minute areas under a very low pressure. In this way it 

 was found that at the margins of the injected area the fluid which 

 had entered the vessels traveled farther than that in the connec- 

 tive tissue spaces, and in many cases the vasa lymphatica were 

 filled beyond the limits of the injected venae lymphaticae, so that 

 in the outermost zone of the injected area the true lymphatics 

 could be readily studied, the venae lymphaticae in this zone being 

 either empty or only partially filled. 



The vasa lymphatica are, for the most part, perivascular chan- 

 nels (fig. 9), but they are also in direct contact with the epithelial 

 walls of the follicles (fig. 10). The vasa lymphatica could not 

 be followed for any great distance through the injected zone, for, 

 on the one hand, they entered the area of opaque injection mass, 

 and in the other direction they ended abruptly, often with a 

 small knob-like dilatation. By means of serial sections I was able 

 to determine in uninjected specimens that the vasa lymphatica 

 opened at the points of terminal dilatation directly into the venae 

 lymphaticae (fig. 10, X). Having demonstrated the connection 

 between the two sets of vessels in uninjected specimens, show- 

 ing the true relation of vasa and venae lymphaticae, many 

 points in the injected specimens could be readily found at 

 which it seemed quite certain that the injection mass was 



