THE LYMPHATIC SYSTEM 



28l 



At first the blood vessels constitute a closed system. The peculiar 

 adult circulation is acquired relatively late. Lifschitz has shown that, 

 in human fetuses between 150 and 300 mm. long, red blood cells are 

 actively formed in the splenic pulp as clusters around the giant cells. 



gastro-hepattc 



Mesogastrium 



'een anlage 



PIG. 289. Two stages in the early development of the human spleen (dorsal is below). A 

 from an embryo of 10.5 mm. (Kollmann); B, from a 20 mm. embryo (Tonkoff). 



The lymphoid tissue of the spleen first appears as ellipsoids about the 

 smallest arteries in fetuses of four months. At seven months, the ovoid 

 splenic corpuscles form as lymphoid nodules about the larger arteries. 

 The capsule, trabecula and reticulum differentiate .from the cells of the 

 common anlage. 



The Glomus Coccygeum. The coccygeal gland is present in 150 mm. 

 (CH) fetuses as an encapsulated cluster of polyhedral cells at the apex 

 of the coccyx. Later it becomes lobulated by the ingrowth of connective- 

 tissue trabeculae and receives a rich vascular supply. According to 

 Stoerck (1906), its tissue at no time resembles the chromaffin bodies, 

 as is often stated. 



