70 OTTO F. KAMPMEIER 
The paired posterior lymph heart is similar in shape to the 
anterior, though somewhat smaller in size at this period (15-mm. 
embryo), and lies lateral to the myotomes in the intersegment 
of the 11th and 12th (fig. 7, cor. lym. post.). It joins the 11th 
intersegmental vein (1/1 v. seg.) which becomes, as shown pre- 
viously,® the proximal portion of the posterior vertebral vein. 
The heart receives the lymph stream from the hinder regions 
of the trunk and the tail through the lateral lymph duct. 
All of the main lymphatic conduits described possess sub- 
sidiaries and capillary plexuses, the ramifications of which in 
frog larvae are admirably shown in injected specimens, as illus- 
trated by Hoyer. 
In the present paper, the origin and development of the pri- 
mary lymph sinus, the jugular lymphatics, and the anterior lymph 
hearts will be considered. The formation of the lymphatics of 
the trunk and tail, including the posterior lymph hearts, will be 
taken up in a succeeding article. 
THE DEVELOPMENT OF THE PRIMARY MAXILLARY LYMPH SINUS’ 
In 5-mm. embryos (Bufo vulgaris) a crude vascular plexus 
exists ventral to the oropharyngeal cavity and has its greatest 
concentration in the vicinity of the thyroid diverticulum. From 
this plexus the external jugulars’ and external carotids and their 
tributaries subsequently differentiate. But at this time veins 
and arteries are still broadly confluent; all channels are alike in 
histological appearance, and merely the definite and constant 
position of certain ones enables us to pick out the future arterial 
and venous components. Farther back towards the heart, how- 
ever, a division has already occurred between them, and the 
external jugulars and carotids are independent, the former curving 
laterally around the ventricle to join the common cardinal veins 
6 Anatomical Record, vol. 9, July, 1920. 
7 A short description of the genesis of the primary lymph sinus in the head of 
Bufo embryos was published by the writer in The American Journal of Anatomy, 
vol. 17, 1915. 
8 In using the term ‘external jugular vein’ the author is following Gruby and 
Ecker; Goette and many other authors refer to this vein as the ‘inferior jugular.’ 
