383 Devi'Idpiiu'iit of the Lyiiiphalic- Xoilo:^ in the Pig 



capillaries; then a stii<ie in which the development of the l)h)oil-vessels 

 determines the pi-imordial follicle. Followinii; the evolution of the artery 

 the adenoid tissue is determined while the lymphatic part of the node, 

 or the sinuses, develops from the proliferation of the lymph ducts, in 

 the pig the adult node still contains some of the lymph plexus which in 

 higher animals is completely transformed into the sinuses. 



Derclopnieni of nodes in the [iriiunrij plexuses. — The other early 

 lymph nodes which drain the skin develop in certain definite areas. If 

 we limit the group to those which receive ducts directly from the skin 

 without passing through other nodes, these glands develop in the long 

 plexus around the external jugular vein in the neck and in the plexus 

 of the inguinal region, and over the crest of the ileum. The develop- 

 ment of the nodes in all of these areas has been studied. These nodes 

 all begin in a plexus of lymph ducts rather than in a lymph sac ; the 

 connective tissue bridges at first show no thickening but soon the nuclei 

 become more crowded and the nodes pass through the various stages 

 shown by the primary lymph node. The node over the crest of the 

 ileum is the simplest, for like the primary lymph node it develops as a 

 single node. The long plexus has the most complicated development 

 and it drains a varied area. In the series at 7 cm. long the entire plexus 

 shows a thickening of the connective tissue bridges. Suhsequently, as 

 shown in Fig. 7, the plexus represents a chain of nodes. In this figure 

 four macroscopic nodes are shown, two at the angle of the jaw, one about 

 the center of the plexus, and the fourth at the lower end of the plexus. 

 Of these nodes the one nearest the angle of the jaw receives ducts directly 

 from the skin of the face around the eye ; the other node receives ducts 

 both from the skin over the head and from the first node. The node in 

 the middle of the plexus receives ducts from man}^ sources, in fact from 

 all of the other glands in the chain and from the front of the neck as 

 well, while the fourth node receives ducts from the fore leg. Thus it 

 will be seen that some of the nodes are secondary or intermediate in the 

 sense of receiving ducts from other nodes. Some nodes, for example 

 those along the internal carotid artery, receive only ducts that have 

 passed through other nodes, that is, they develop along the etferent ducts 

 of a node, while some receive ducts both directly from the skin and 

 from other nodes. In short, a gland may be secondary for some ducts 

 and primary for others. 



The histogenesis of these various nodes follows the same general lines 

 as the primary lym])h nodes, beginning witli the stage represented in 

 Fig. 10, but there is the widest possible variation in the relative pro- 



