302 GEO. S. HUNTINGTON 



It is now possible to directly compare conditions observed in 

 embryos of the different vertebrate classes during the development 

 of the lymphatic system, without being led astray by the signal 

 divergences encountered. Thus Miller's account of the devel- 

 opment of the avian thoracic duct repeats, on a large and impres- 

 sive scale, the above described stages in the development of the 

 maimnalian jugular sacs and primitive ulnar lymphatics. In the 

 further course of development the early haemophoric axial lym- 

 phatics of the bird are retained in the permanent lymphatic 

 organization as the main systemic lymphatic channels of the 

 thoracic ducts. In the manmial the longer cephalic segment of 

 the primitive ulnar channel, after fulfilling its earlier haemo- 

 phoric function, atrophies and disappears, while the distal por- 

 tion, becoming the axillary lymphatic sac, serves at first as an 

 extensive temporary lymphatic reservoir, and then becomes in- 

 corporated in the system of the permanent lymphatic drainage 

 of the body wall and anterior limb. 



2. A second fact, which appears to me to be of great physio- 

 logical and structural importance, is the establishment, in cer- 

 tain areas of the embryo, of large temporary lymphatic receiving 

 chambers or reservoirs, in which the interstitial fluids of the 

 developing embryo are apparently stored pending the completion 

 of lymphatic channels and connections through which this fluid 

 is eventually turned into the plasma-stream of the venous 

 circulation. 



The axillary or subclavian reservoir above described is a very 

 pregnant instance of this condition. Its early connection, dorsal 

 to the brachial plexus, with the jugular lymphsac during the 

 haemophoric period, the subsequent interruption of this com- 

 munication, the ensuing enormous fluid distension of the sac, 

 and finally its secondary drainage through the chain of sub- 

 clavian lymphatics developed caudoventral to the brachial plexus, 

 are all definite and constant phases which in combination with 

 each other furnish a very clear and significant picture. 



In part these lymphatic ontogenetic stages are without doubt 

 closely associated with and dependent upon the rearrangement 

 of the main venous lines of the neck, thorax and anterior limb. 



