100 THE ESSENTIALS OF HISTOLOGY 



LESSON XXII. 



LYMPHATIC GLANDS, TONSIL, THYMUS. 



1. SECTIONS of a lymphatic gland which has been stained in bulk with magenta 

 and embedded in paraffin. 1 Notice (1) the fibrous and muscular capsule, with 

 trabeculse extending inwards from it through the cortex and anastomosing with 

 one another in the medulla, (2) the dense lymphoid tissue (adenoid tissue of 

 authors) forming large masses in the cortex (cortical nodules) and rounded 

 cords in the medulla (medullary cords). Notice also the clearer channel or 

 lymph-sinus which everywhere intervenes between the fibrous tissue and the 

 lymphoid tissue. Observe the fine fibres and branched cells which bridge 

 across this channel. 



Make a general sketch under a low power of a portion of the cortex 

 together with the adjoining part of the medulla, and under a high power 

 drawings of small portions of cortex and medulla. 



2. In sections of tonsil prepared similarly to those of the lymphatic gland, 

 notice the large amount of lymphoid tissue only imperfectly collected into 

 nodules. Observe also that the stratified epithelium, which covers the mucous 

 membrane here as elsewhere in the mouth, is infiltrated with lymph-cor- 

 puscles. Here and there pit-like recesses may be met with glands opening 

 into the pits. 



3. A similar preparation of the thymus gland of an infant. Notice that 

 the masses of lymphoid tissue which form the lobules of the gland are 

 separated by septa of connective tissue, and that they show a distinction into 

 two parts, cortical and medullary. Observe the differences of structure of 

 these two parts, and especially notice the concentric corpuscles in the 

 medullary part. 



Make a sketch of one of the lobules under a low power and of a small part 

 of the medulla under a high power, including one or two concentric corpuscles. 

 Measure the latter. 



Structure of a lymphatic gland. A lymphatic gland is composed 

 of a, fibrous and muscular framework, which encloses and supports the 

 proper glandular substance, but is everywhere separated from it by a 

 narrow channel, bridged across by cells and fibres, which is known as 

 the lymph-channel. The framework consists of an envelope or capsule 

 (fig. 124, c), and of trabeculce (tr\ which pass at intervals inwards 

 from the capsule, and after traversing the cortex of the gland divide 

 and reunite with one another so as to form a network of fibrous bands. 

 At one part of the gland there is usually a depression (hilus), and at 

 the bottom of this the medulla comes to the surface and its fibrous 

 bands are directly continuous with the capsule. 



1 See Appendix. 



