LYMPHATIC ORGANS 185 



The lingual and pharyngeal tonsils begin their development during the 

 later months of intra-uterine life. In the pharyngeal tonsils, definite nodules 

 appear about the time of birth or during the first or second year. In the 

 lingual tonsils the nodules are not fully formed until the fifth or sixth year. 



TECHNIC 



Normal human tonsils are so rare, owing to the frequency of inflammation of 

 the organ, that it is best to make use of tonsils from one of the lower animals (dog, 

 cat, or rabbit). Treat as in technic i, p. 176, care being taken that sections pass 

 longitudinally through one of the crypts. 



The Spleen 



The spleen is a lympliatic organ and might be quite properly 

 classed as a hasmolymph node. Its peculiar structure appears to 

 depend largely upon the arrangement of its blood-vessels. 



e 



Fig. ioq. — Section through Portion of Cat's Spleen, to show general topography. 

 X15. (Technic i, p. i^i.) a, Capsule; b, septa containing blood-vessels; c, center 

 of lymph nodules; d, septa; e, germinal centres. 



Except where attached, the spleen is covered by a serous mem- 

 brane, the peritoneum (page 272) . Beneath this is a capsule of fibrous 

 tissue containing numerous elastic fibres and some smooth muscle 

 cells. Along the broad attached surface this capsular connective 

 tissue blends with the connective tissue of the posterior abdominal 

 wall. From the capsule strong connective-tissue septa, similar to 

 the capsule in structure, extend into the interior of the organ. These 

 branch and unite with one another to form very incomplete anas- 

 tomosing chambers. At one point on the surface of the spleen known 

 as the hilum a deep indentation occurs. This marks the entrance 



