98 NORMAL HISTOLOGY. 



THE SPLEEN. 



The spleen has the structure of a large lymphatic node. It con- 

 sists of a capsule and splenic pulp. The capsule consists of two 

 coats an outer serous and inner fibrous coat. Extending from 

 the capsule into the piilp are trabeculw, which divide and subdi- 

 vide, forming a reticulum of connective tissue. The splenic pulp 

 comprises the loose adenoid tissue and the dense adenoid tissue. The 

 dense adenoid tissue is disposed in spherical masses which are situ- 

 ated in the forks of the arteries. Each mass is pierced by an ar- 

 tery. These dense spherical masses of the pulp are called Malpighi- 

 an corpuscles. Their structure does not differ materially from that 

 of the loose tissue. The pulp, as with other lymphatic structures, 

 consists of a connective tissue reticulum, holding in its meshes leu- 

 cocytes, red corpuscles, lymph oid cells, and pigment granules. 



THYMUS BODY. 



This structure is derived from the hypoderm, and in its early 

 development is chiefly epithelial in character, but later becomes in- 

 vaded with mesodermic tissues, until it assumes a lymphatic type. 

 After the second } r ear it loses its characteristic structure, and its 

 tissues are replaced by fibrous tissue and fat. It consists of a cap- 

 sule and a pulp, which is divided into lobes. The lobes are separated 

 from each other by septa derived from the capsule. The lobes are 

 divided into lobules, each lobule consisting of adenoid tissue, the 

 outer, looser portion being called the cortex, while the inner, denser 

 portion is the medulla. Hassal's corpuscles are masses of em- 

 bryonic epithelial cells found in the medulla, 



TONSILS. 



The tonsils are composed of diffuse adenoid tissue, containing 

 from ten to eighteen lymph follicles. There is a fibrous capsule, be- 

 neath which are the connective tissue reticulum, the lymphatic fol- 

 licles, mucous glands between the follicles, and lymphoid cells. 



Laboratory exercise No. 29. The spleen. Harden in Erlicki's fluid 

 or alcohol, embed in paraffin, and stain with haematoxylin and eosin, 

 method No. 8. Examine, first, the capsule, and its extensions, or tra- 

 beculae, penetrating the splenic pulp. Distinguish between the loose 

 and dense adenoid tissue. Examine the structure of a Malpighian cor- 

 puscle with H. P., noting the connective tissue reticulum and the 

 lymphoid cells. Describe the disposition of arteries, veins, and lym- 

 phatics in the spleen. Has the spleen a duct? Drawings. 



