242 PRACTICAL HISTOLOGY. [XX. 



(d.) A variable number of concentrically-striated bodies, con- 



FiQ. 229. In jected Lobules of Thymus 

 of a Cat. a. Cortex ; b. Medulla ; 

 c. Blood-vessels ; d. Septum of 

 connective tissue. 



FlG. 230. Elements of the 

 Thymus Gland, a. Leu- 

 cocytes ; b. Concentric 

 corpuscle, x 300. 



centric corpuscles or HassaLTs corpuscles. 



amongst the adenoid tissue (fig. 230). 



Sections of capillaries 



THE SPLEEN. 



The spleen, like the thymus, thyroid, and some other glands, 

 is a " ductless gland," and is invested by a fibrous capsule. The 

 capsule consists of an outer layer of connective tissue covered by 

 endothclium the serous or peritoneal covering and a deeper 

 layer of connective tissue with networks of elastic fibres, and in 

 some animals (dog, cat, pig) smooth muscular fibres. From the 

 deeper surface of the latter flattened or rounded trabeculse pass into 

 the organ, and as they do so they branch and nastomose, thus 

 forming a spongy mesh work with a labyrinth of communicating 

 spaces. These spaces are filled with a -reddish-purple soft substance, 

 the splenic pulp. The blood-vessels are ensheathed by connective 

 tissue, to which the trabeculse are attached. The red colour of the 

 pulp is due to the large number of blood-corpuscles. The trabe- 

 cular framework is continuous with the connective tissue entering 

 the organ along with and covering the blood-vessels " adventitial 

 sheath " at the hilum of the organ. In the splenic pulp are small 

 spherical whitish bodies Malpighian corpuscles (0.2-0.7 mm.). 

 The Malpighian corpuscles are small groups of leucocytes de- 

 veloped here and there in the adventitia of the splenic artery. 



