46 Florence R. Sabin. 



system in chick embryos. Basing his work on Budge's, he worked 

 out with care the origin of the posterior lymph hearts which Budge 

 had discovered. He found that the posterior lymph hearts begin at 

 the middle of the seventh day in connection with the lateral branches 

 of the first five coccygeal veins. He says that corresponding to these 

 veins there are excavations in the mesenchyme which soon enter into 

 communication with the lateral branches, and in fact one would say 

 that these fissures are simply dilatations of the veins themselves. 

 These two statements of course exclude one another, for the spaces can 

 not be both fissures in the mesenchyme and dilatations of the veins. 

 C'Esaminando in serie le sezioni caudali di un emb. di g. 6 + oi'6 

 18, si scorge che nel mesenchima che sta lateralmente ai miotomi ed 

 in corrispondenza dei rami laterali delle prime cinque vene coccygei, 

 si vanno scavando dei piccoli spazi o fessure che ben presto entrano 

 in comunicazione cogli stessi rami laterali venosi : si direbbe anzi che 

 esse non sono che semplici dilatazioni, ramificazioni delle stesse 

 vene.") 



Then he describes these fissures as becoming more abundant and 

 confluent. By opening up communications with each other they 

 form a sac or lymph heart in the mesenchmye. This sac he says is lined 

 with flattened mesenchyme cells, which, if it were so, would, according 

 to our standpoint, exclude it from being a vein. He found muscle in 

 the wall of the hearts on the ninth day and was able to inject the 

 heart directly by the second half of the tenth day. Sala's description 

 of the origin of the posterior lymph hearts in the chick is so clear 

 and graphic that it is perfectly evident to those who are familiar 

 with the method of origin of the lymph sacs in mammals, that the 

 two processes are the same, that the sacs arise from the veins in both 

 cases. The fact that Sala had the old conception of the lymphatic 

 system as coming from the tissue spaces too firmly fixed in mind 

 to really accept the evidence of his own material does not need to 

 confuse the picture. 



The lymphatic ducts he thought began as fissures in the mesenchyme 

 along the hypogastric veins on the ninth day. By the eleventh day 

 these spaces communicated and formed a plexus of lymphatic 

 ducts which connected with the lymph hearts and the thoracic duct. 



