The Lymphatic System in Hum,an Embryos. 



65 



vessels representing the forerunners of the lymphatics being much 

 larger on the right side than on the left. The three largest sacs of 

 this series measure .27 x .19 mm., .36 x .14 mm. and .27 x .14 mm. 

 respectively. 



The next specimen is an embryo (No. 109) measuring 10.5 mm. 

 In this embryo there are symmetrical jugular sacs as seen in Fig. 3, 

 just external to the internal jugular vein. The relation of the sac 

 to the venous system as a whole is shown in Fig. 4, which is a 

 reconstruction from serial sections. This embryo has been figured 



^^W^^^. 

 ^^M^ 



Fig. 3. Transverse section through the neck of a human embryo, 10.5 mm. 

 long, showing the symmetrical jugular lymph sacs. Mall collection. No. 

 109. A., artery ; N. X., n. vagus ; m. s., n. sympatheticus ; Oe., oesophagus ; 

 P., pericardium ; S. 1. j., saccus lymphaticus jugularis ; T. trachea. The V. 

 jugularis are filled with blood and lie just medial to the sacs. 



by Bardeen and Lewis, American Jour, of Anat., Vol. I, 1901-1902, 

 and by Dr. Mall, American Jour, of Anat., Vol. IV, 1905 ; the 

 outline and some of the details of the figure are taken from their 

 reconstructions. As will be seen in Fig. 4, the sac lies external to 

 the jugular vein and anterior to the primitive ulnar. In this embryo 

 the question of a valve is an interesting one. 



In studying through Dr. Mall's collection it has proved that the 

 finding of the valves depends wholly on the plane of the section. 

 There is only one plane which is at all adequate for determining the 



