374 



The Development of the Lymphatic System 



made from two points, marked a for the neck and c over the crest of 

 the ileum. The letters are used to mark the area which can be injected 

 in a pig of a given size. For example, c corresponds to a pig 3 cm. 

 long and shows that the ducts are just beginning over the crest of the 

 ileum, while from the neck they have already grown over the head and 

 thorax, and over the face either side of the eye. 



The areas without any ducts 

 in the diagram represent the 

 areas which have not received 

 lymphatics in a pig 4 cm. long. 

 In a pig 5.5 cm. long the two 

 systems of ducts s~hown in the 

 diagram have met and anasto- 

 mosed over the body wall, and 

 ducts have grown down the legs 

 nearly to the feet, but there are 

 still areas of the skin which 

 have not yet received lymphat- 

 ics; for example, the top of the 

 head, the foot pads and the tail. 

 The details of how these areas 

 receive lymphatics as well as the 

 relation of these ducts to the 

 glands that form subsequently 

 are given later in order to relate 

 them to the lymph hearts. At 

 this time we will limit the atten- 

 tion to the study of the succes- 

 sive zones of lymphatics and 

 their relation to the areas with- 

 out lymphatics. 



The method of obtaining these injections is important. In the neck 

 it was found that the best way to obtain maximum injections was to 

 introduce the needle perpendicular to the skin, and it appeared later 

 that this is due to the fact that one often enters the cervical lymph 

 heart, a large sac from which all the ducts radiate. The method used 

 was as follows : A glass tube drawn out to a fine point, the size of which 

 should vary with the size of the pig, is held in a firm clamp which can 

 be moved in three directions by screws. The glass tube is connected 

 by rubber tubing with a flask of Berlin blue or India ink, and this flask 

 is again connected with a pressure flask. The pig is placed on the 



Fig. 1. Composite picture of the spreading of 

 the superficial lymphatics in the embryo pig. 

 A, area of lymphatics in a pig 18 mm. long ; b, 

 area in a pig 2 cm. long; c, area in a pig 3 cm. 

 long ; d, area in a pig 4 cm. long. 



