OF THE LYMPHATIC SYSTEM OF THE CHICK. 471 



the axilla could be injected. In fact, the hole was of such a nature that there was no 

 skin or subcutaneous tissue present for vessels to grow in. However, when the 

 body-wall, between the gap and the posterior limb, was tested in such an embryo, 

 a normal lymphatic plexus was injected in every instance. This extended anteriorly 

 as far as the edge of the gap but could not be injected any farther. In such speci- 

 mens (chicks of 5 to 5 days) the posterior lymphatics were normal and were present 

 in the lymph-heart region and near it; no lymphatics were injected over the pelvis. 

 This condition is shown in figure 6 and can be compared with figure 5, showing the 

 injected lymphatics of a normal chick of the same stage. Injection of lymphatics 

 on the opposite (unoperated) side showed a similar condition, both in character and 

 extent of the lymphatic plexus, except for the fact that axillary lymphatics, con- 

 necting the side lymphatics with the deep plexus, were present. 



The fact that the side plexus in such operated specimens develops in the same 

 region and at the same time as in normal embryos, and at a period before any growth 

 from the posterior point of origin could have taken place, coupled with the fact of 

 its completely normal appearance, speaks for the existence of another normal point 

 of origin for the superficial lymphatics of the chick. 



Observation of normal chicks at early stages (5 days and under) showed a 

 stage in which a number of knobs of stagnant blood are present in that part of the 

 lymphatic plexus of the side region just anterior to the leg. By injection these 

 knobs were found to connect with a number of veins lying parallel to each other, 

 which at this stage flow ventrally, encircling the abdomen. These veins are transi- 

 tory; in chicks of 5| days they disappear and the drainage for this region is all 

 anterior, through the newly developed thoraco-epigastric vein a stage at which 

 a definite lymphatic plexus can be injected for the length of the side, with deep con- 

 nections through the axilla with the jugular lymph-plexus. At this 5^-day stage 

 and later no connections can be injected between these lymphatics of the side 

 plexus and the neighboring blood-vessels. 



It is also evident from these experiments that the regions in which lymphatic 

 vessels retain their venous connections during all or part of embryonic life are not 

 the only points of origin for the lymphatic system. 



OPERATION 3. ISOLATION OF THE LEG AND PELVIS. 



The foregoing experiments gave only a partial answer to the problems in which 

 we were interested. We therefore tried to develop an operation for isolating com- 

 pletely a region supposed normally to be supplied by ingrowth from some point or 

 region of origin. For this purpose we operated on chicks toward the second half 

 of the third day of incubation (embryos averaging 2 days and 17 hours), removed 

 the tail region as in operation 1, and also dissected out the five or six somites pos- 

 terior to the omphalo-mesenteric vein and the adjacent body- wall on the right side. 

 By this means we succeeded in obtaining embryos without tails (with the posterior 

 point of origin removed) in which a gap had been made on one side, isolating the 

 leg and pelvis from the anterior lymphatics, and in which the probable point or 

 region of origin anterior to the leg had been removed. More than a dozen chicks 

 survived this double operation. 



