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Fig. 10 From a photograph of a transverse section through the thoracic region 

 of a chick embryo of eight days and fourteen hours. /, Precardinal vein; 5, jugular 

 lymph sac with tap, at 5a, on the dorso-mesial side of the precardinal vein; 7, 

 oesophagus; 9b, vagus nerve; 17, pleural cavity. 



chick embryos show that it develops in this form in exact agree- 

 ment with the corresponding mammahan ontogenetic stages. 

 It is therefore probable that careful examination of the anterior 

 lymphatico- venous connections of the adult bird will demonstrate 

 the persistence of the sac in a modified form, as has been shown to 

 be the case in the mammal. 



