76 PRACTICAL HISTOLOGY. 



THE LYMPHATIC SYSTEM. 



THE lymphatic vessels consist of capillaries and trunks of variable size. The capillaries con- 

 sist of single layers of squames with characteristic sinuous edges, and the larger vessels have 

 a structure resembling veins with three coats, but the walls are very much thinner. They 

 have valves in their course. 



LYMPHATICS OF THE DIAPHRAGM. 



PREPARATION (L). Kill a rabbit or guinea-pig by bleeding. Tie a ligature round the 

 inferior vena cava and the gullet, and remove the abdominal viscera, so as to expose the under 

 surface of the central tendon of the diaphragm. With a fine camel-hair pencil, brush away 

 the epithelium covering it, and then silver it in the usual way (p. xlv). After exposure to 

 light mount a small piece in dammar. 



EXAMINATION (L). Observe the network of lymphatic vessels, some with a small, 

 others with a large lumen. Trace the course of a large vessel, and observe the bulgings in its 

 course with narrower parts between (PI. XVII., Fig. i). Especially at the division of a vessel 

 a valve may be seen.- (H). Study the character of the epithelium lining the vessels, and notice its 

 sinuous outline. 



Lymphatics of the Intestine. For a large class, silvered lacteals are readily seen in the 

 preparation of silvered muscular fibre obtained from the small intestine of a rabbit (p. 37). 

 Refer to that preparation, and observe details in the structure of these vessels similar to those 

 described in the lymphatics of the diaphragm. 



The lymphatics communicate with the serous cavities by means of small apertures stomata 

 guarded by small granular cells. The stomata are most easily obtained from the septum of 

 the great lymph-sacs of the frog, though they may also be obtained by silvering the under 

 surface of the diaphragm of a rabbit. Behind the stomach and on each side of the vertebral 

 column of the frog there lies a large lymph-sac, separated only from the peritoneal cavity by a 

 very delicate membrane or septum, which is perforated by small apertures stomata which 

 bring the two cavities into direct communication. 



SEPTUM CYSTERN^E LYMPHATICS MAGNS. 



PREPARATION. Kill a frog and carefully remove the abdominal viscera, taking care not 

 to injure the fine septum above described. Pour distilled water over the posterior ab- 

 dominal wall immediately behind the stomach, when a delicate membrane will be floated 

 up and brought into view. Pour over it a half per cent, solution of nitrate of silver till it 



