The Lymphatic System in Human Embryos. 45 



mass of embryonic connective tissue which has no lymphatics. The 

 fluid rnns out in the lines of least resistance, simulating performed 

 canals but easily distinguished from true lymphatic capillaries, both in 

 form and from the fact that as the injection proceeds the network 

 fills into a solid mass. Serial sections of the area vasculosa showed 

 no preformed channels, but rather that the space between the germ 

 layers is bridged by delicate fibrils, the processes of mesenchyme 

 cells. It seems certain then that Budge's primitive lymphatic system 

 is simply a study of the extent of the early coelom and morphologi- 

 cally has no relation to the lymphatic system. 



In the understanding of the lymphatic system this point is of great 

 importance, as will be shown later. Kone of the serous cavities, 

 hollowed out of the mesenchyme, that is, the pleural and peritoneal 

 cavities, the joints, the various bursse, and the chambers for the 

 vitreous and aqueous humors in the eyes, though they contain serous 

 fluid ever form a part of the true lymphatic system. In Budge's 

 second paper, which is unfortunately just a fragment of his work 

 published from the notes after his death, are pictured beautiful 

 figures of true lymphatic injections made at a much later stage, 

 namely in embryo chicks, 18 days old. These, the true lymphatics, 

 Budge thought belonged to a second, the permanent system, distin- 

 guished from the first by the presence of the thoracic duct which 

 emptied into the veins. Budge thought that the thoracic duct arose 

 from spaces derived from the ccelom. He also discovered the pos- 

 terior lymph hearts in chick embryos between 10 and 20 days old. 



The theory of the origin of the lymphatic system from tissue 

 spaces was further illustrated by Gulland.^ 



He found spaces hollowed out in the mesenchyme along the course 

 of the blood vessels of the limbs and thought that these flowed to- 

 gether to form ducts. 



The next exponent of the theory that the lymphatics arise from 

 the tissue spaces in Sala.^ 



Sala has studied the origin and the development of the lymphatic 



^Gulland. Journal of Pathology and Bacteriology, Vol. II, 1894, p. 466. 

 "Sala. Ricercbe Lab. di Anat. Norm. d. r. Univ. di Roma, Vol. VII, 1899-1900. 



