280 TEXT-BOOK OF EMBRYOLOGY. 



ing vessels constitute the anlagen of lymph glands (Fig. 255). The new cells 

 which appear in the masses are lymphocytes which may pass through the walls 

 of the neighboring blood vessels and lodge here or may be derived directly from 

 connective tissue (mesenchymal) cells in situ Whatever the origin of the 

 lymphocytes may be, they have the opportunity here to divide freely. The 

 mass becomes still more cellular and enlarges at the expense of the lymphatic 

 vessels which then come to form a network around the mass. This network is 

 the marginal plexus, and it communicates freely with the neighboring lymph- 

 atic channels. Within the mass of cells blood vessels are present from the begin- 

 ning, and these are destined to be the blood vessels of the lymph gland, and the 

 point of their entrance and exit marks the hilus. Outside of the marginal 



- Hilus 



,;.,'. .,^'-^^ff^4&%. , ;> ; ,n 



'' j.... -Marginal sinus 



-Capsule 



FIG 256. From a section through the axilla of a human embryo of 125 mm. (4-5 months), 

 showing an early stage of a lymph gland. Kling. 



plexus the connective tissue condenses to form the capsule. The gland at this 

 stage thus consists of a central compact cellular mass, made up of connective 

 tissue and lymphocytes, in which blood vessels ramify; a plexus of lymphatic 

 channels around the mass which communicate with the neighboring channels; 

 and around the whole structure a capsule of connective tissue (Fig. 256). 



Further development consists of the breaking up of the cell mass by lymph- 

 atic channels and the formation of the follicles. It seems probable that 

 branches from the marginal plexus invade the cell mass principally from an 

 area around the hilus, thus breaking it up into smaller irregular masses or cords. 

 At the side opposite the hilus the invading channels are less numerous, leaving 

 larger parts of the mass which become the follicles (nodules) of the cortex. On 

 all sides the invading channels communicate with the marginal plexus and form 

 the so-called intermediary plexus. The gland as a whole enlarges and its per-. 



