30 HENRY MCELDERRY KNOWER 



supra-branchial tissues of the temporal region, to end at the 

 lateral margin of the submaxillary plexus of blood vessels. 

 The fine caliber of the distal section and growing tip is evi- 

 dently a structural character of these early centrifugal proc- 

 esses, and no failure of injection. In figure 6 a special 

 delicacy and completeness for this stage in the injection of 

 this duct as compared with other vessels, has brought out its 

 character as a delicate plexiform channel in the entire length, 

 continuous from the lymph heart plexus through the temporal 

 region to the lateral border of the submaxillary area. The 

 small pointed projections which extend from the outer edges 

 of this tract, from the subocular process, and from the irregu- 

 lar distal extremity, are constant features of peripheral 

 lymph vessels. In stronger injections the projections would 

 appear as longer lateral or terminal filaments. 



The posterior lymphatics of the second period 



The lymphatics behind the lymph heart, like those in front, 

 grow out as extensions of the lymph heart plexus, and estab- 

 lish typical dorsal and lateral systems connected throughout 

 in the early stages. Thus the lateral lymphatic plexus in 

 figure 5 is a posterior continuation of the heart vessels super- 

 ficial to the segments behind the third, with a somewhat 

 stronger path developed along the lateral line, the vessels of 

 the net spreading dorsally and ventrally from it. However, 

 the impression that the lateral line tract is typically a single 

 vessel, as it appears at times (fig. 6) proves, on comparison 

 with the more complete details in figure 5, to be merely a not 

 uncommon result of incomplete injection. It is evident that 

 if only small portions of the ventral plexus are entered by 

 the injection, while the upper vessels are conspicuously dis- 

 tended from front to back as here, an apparently single vessel 

 may result, as shown in figure 6 (see also fig. 7). The sinuous 

 or undulating course and plexiform character of the injected 

 tract is therefore, of course, merely the result of a variation 

 in the technique. 



