160 PRACTICAL HISTOLOGY. 



and fastened with needle points to the small piece 

 of cork on either side of the slit. Before the rest 

 of the operation is described, a word or two may he 

 said with regard to the structure of the organ. It 

 is not solid throughout as in mammals, but hollow, 

 the interior being occupied by a lymphatic cavity. 

 This lymph space is traversed by bundles of muscu- 

 lar fibres (Fig. 27, m) which pass towards the ex- 

 tremity of the organ and are connected to the sides 

 by delicate septa of connective tissue (s s). Above 

 the lymph space in the present position of the 

 animal on its back with the tongue extruded the 

 mucous membrane is thick and papillated (Fig. 27, 

 A, a a). Below is a very thin and delicate mucous 

 membrane (/>), with numerous bloodvessels, and small 

 muscular fibres running over it. The former mem- 

 brane is too thick and irregular to allow the delicate 

 internal structures to be seen through it ; it is there- 

 fore slit up longitudinally and pinned to either side. 

 But to do this without injuring tbe delicate parts 

 below, it must be separated from them, and this can 

 best be effected by distending the lymph sac with 

 salt solution. With this object a Pravaz syringe 

 (Fig. 17), provided with a fine and sharp canula, is 

 filled with the fluid, and its point is stuck into the 

 tongue near the end, passing about half an inch 

 backwards. It will almost certainly be found that 

 on pressing the piston down, the salt solution will 

 readily flow into the lyrnph sac, and as it fills this 

 will cause the thin mucous membrane at the lower 

 part to become bagged out, and completely separated 

 from the muscular bundles, m m, and these again 

 from the thick layer above. The latter is now care- 

 fully slit up along its middle by sharp fine scissors, 

 and first one edge of the wound and then the other 

 is drawn to the side of the slit in the cork and 

 fastened there by two or three needle-points. If 

 everything is carefully done, there will be no escape 

 of blood over the preparation ; but should any blood 



