Thr Oviijin and Development of the Lymphatic System. 21 



shows in fig. I-m (Evans 35). Each of the five spinal veins drains 

 ,1 plexus of w i 1 1 1 ■ capillaries, which marks the presence of the develop- 

 ing spina] ganglia. 



It is. however, the superficial veins which arc of more interest from 

 the standpoint of the lymphatic system. Along the dorso-lateral bor- 

 der of the cardinal veins there is a series of intersegmental sprouts, 

 varying from one to four or five in each interspace. These sprouts 

 drain a superficial capillary plexus which is developing in a groove 

 in the neck which is a continuation of the groove dorsal to the Wolffian 

 ridge. The arteries fur this superficial capillary plexus come from the 

 deep segmental arteries (Evans 35, fig. 137). The connections of 

 the plexus with the cardinal vein are most abundant near the poste- 

 rior cerebral vein. This superficial capillary plexus of the body wad 

 has a most interesting development. For the area between the limb 

 buds it has been worked out by Dr. Helen W. Smith (111), whose 

 figures are copied by Evans (35). This superficial plexus in the tail 

 region shows a constant zone of widened capillaries (35, fig. t61 i 

 corresponding to the position of the posterior lymph hearts in birds. 

 For the neck region it is necessary to know this plexus in order to 

 locate the jugular lymphatics, and therefore its development will be 

 followed in further stages. 



The ventral branches of the anterior cardinal vein are represented 

 at this stage by one large pericardinal vein, which receives branches 

 from the gill arch region. The common stem for the branchial and 

 pericardial vessels connects with the anterior cardinal vein, but it 

 drains directly into the duet of Cuvier (see Grosser and F. T. Lewis 

 as quoted by Evans 35, p. 660) on the right side of this embryo, 

 while on the left side of the same specimen it opens into the anterior 

 cardinal vein. 



The earliest lymphatic buds have been found in embryo pigs 

 measuring from Ki to 11 nun. lone-. All of my measurements mean 

 the greatesl length and are made on the fresh specimen. The stage 

 of the first lymphatics is shown in two figures, fig. 5, a total mount 

 of an embryo injected with India ink through the umbilical artery 

 in a specimen 11 mm. long, and fig. 6, a cross section 250 /i thick. 

 through the lymphatic area in an embryo measuring 11 mm. The 

 blood vessels were injected with India ink, and the lymphatics are Idled 

 with blood. 



