Cervical Veins and Lymphatics in Human Embryos. 39 



earliest forerunners, perhaps, of the lymphatic system in man."^^ 

 The vessels in question are clearly veins. 



In the 11.5 mm. embryo (Fig. 2) there are four or perhaps five 

 lymphatic spaces, apparently separate from each other. They con- 

 tain some blood corpuscles and in two cases they seem to connect 

 with the vein, but the apertures are very small. At 16 mm. (Fig. 3) 

 the lymphatics have increased and extend along a considerable por- 

 tion of the anterior cardinal vein. There is a separate space in 

 relation with the linguo-facial vein. A lymphatic vessel extends from 

 the jugTilar sac dorsal to the brachial plexus, but the dorsal subclavian 

 vein which it accompanied in the earlier stage has disappeared. 

 Similarly in the rabbit the dorsal subclavian vein is accompanied by 

 a lymphatic vessel and later both vein and lymphatic disappear, ^o 

 outlet from the jugular sac into the cardinal vein was found in the 

 transverse sections studied, but, as Professor Sabin has recently 

 demonstrated, frontal sections are more favorable for detecting the 

 valvular orifice. In an embryo o£ 22.8 mm. (Fig. 4) there is a very 

 large jugular sac which has grown around certain nerves. The upper 

 small aperture transmits a branch of the third cervical nerve, and 

 the lower one is for branches of the third and fourth. In a rabbit 

 of 14.5 mm. the jugular sac showed similar openiugs for the third 

 and fourth cervical nerves. 



Eeturning to the veins in Fig. 3, it will be seen that the branch 

 of the primitive ulnar vein near the elbow now joins the radial 

 extremity of the ulnar vein, and from their junction a vessel can be 

 followed along the radial border of the limb toward the shoulder. It 

 is very probable that at this stage there is a capillary union between 

 this cephalic vein and the lateral branch of the anterior cardinal 

 which is shown in the figure. An obvious connection between 

 them is seen in Fig. 4. Here the lateral branch of the anterior 

 cardinal may be identified as the external jugular vein and it can 

 be traced upward behind the ear as the posterior auricular vein. It 

 does not yet connect with the linguo-facial vein. 



Fig. 4 shows the brachial vein (derived from the primitive ulnar) 

 joining the larger thoraco-epigastric vein to make the (ventral) sub- 

 clavian vein. Along the latter, scA^eral branches anastomose to make 



^^Ingalls. X. W. A contribution to the embryology of the liver and vascular 

 system in man. Anat. Record. 190S, Vol. 2. p. 343. 



