278 



TEXT-BOOK OF EMBRYOLOGY. 



become relatively reduced in size during later development, although in the 

 adult there is fairly well marked dilatation. 



The first studies by Sabin on the developing lymph sacs or hearts in the 

 pig led to the conclusion that they were outgrowths from the large veins. Sub- 

 sequent reasearches on the rabbit by Lewis, who was the first investigator to 

 furnish the clue for the proper interpretation of the mammalian jugular lymph 

 sacs, and by Huntington and McClure on the cat, have resulted in practical 



Ant. cardinal vein !• 

 Subclavian vein 



Post, cardinal vein 

 Diaphragm. 



Suprarenal gland 

 Mesonephros 



Kidney- 



Ant, lymph heart 



Deep lymphatics 



of arm 



Branches to heart 



Branches to lung 



Aorta 



Branch to oesophagus 



Branches to stomach 



Branch to duodenum 



Branches to mesenteric plexus 

 Cisterna chyli 



Post, lymph heart 



Deep lymphatics 

 to leg 

 *i / 1/ v '■ 



Fig. 254. — Diagram showing the arrangement of the lymphatic vessels in a 

 pig embryo of 40 mm. Sabin. 



unanimity of opinion that the structures in question are derived directly from 

 veins, but are not outgrowths from the large venous trunks. 



So far as the development of the lymph sacs or hearts in other vertebrate 

 forms is concerned, the excellent work of Sala on the caudal lymph hearts in the 

 chick, the observations of Mierzejewski and others on the jugular lymph sacs 

 in the chick, and the careful and thorough investigations of Huntington on the 

 caudal and jugular lymph sacs in reptilian forms, all illustrate the general 

 principle that the lymph sacs or hearts are direct venous derivatives and that 

 there is a decided uniformity in the manner of development of these homol- 

 ogous structures in the different vertebrate classes. 



