LYMPHATICS, ETC , OF THYROID GLAND OF THE DOG. 207 



I, The Lymphatics. 



Methods. — The methods of investigation adopted were as — 



(1) Injection with Berlin Blue. — The thyroid gland of a 

 freshly-killed dog was injected in situ with a solution of 

 Berlin blue by the method of puncture with a subcutaneous 

 syringe. When sufficiently injected the gland was removed 

 and hardened, and sections of it were stained and mounted 

 in balsam. 



(2) Injection with Nitrate of Silver. — The gland was in- 

 jected in a similar manner with a one eighth per cent, 

 solution of nitrate of silver instead of Berlin blue. 



Throughout this research the glands examined were those 

 of adult dogs only. 



Characters and Distribution. — The appearances presented 

 by the lymphatics may be considered under two heads : 



1. Macroscopic Appearances. — On injecting one of the 

 portions of the gland with Berlin blue solution by the above 

 method the following appearances presented themselves : — • 

 The whole organ swelled up and a fine network of injected 

 vessels appeared on the surface, which could be distinctly 

 seen with a hand-lens ; at the same time lymphatic vessels 

 became injected, running from the gland in a direction 

 upwards and downwards. The former, after forming a 

 plexus above the gland, gave off two principal branches, the 

 one running upwards and inwards over the front of tlie 

 windpipe, the other upwards and outwards, and terminating 

 in a large lymphatic gland situate under the upper part of 

 the sterno-mastoid muscle. The vessels running downwards 

 from the gland emerged at the lower and inner extremity of 

 the organ, and soon united to form a single vessel, which, 

 taking a course downwards and inwards in front of the 

 trachea, enteied a small lymphatic gland situate in the 

 median line over about the sixteenth ring of the trachea. In- 

 jection in a similar manner with nitrate-of-silver solution 

 also showed a network of lymphatics on the surface of the 

 organ. 



2. Microscopic Appearances. — Traversing the gland 

 chiefly in a longitudinal direction, and accompanying the 

 larger blood-vessels and septa of connective tissue are nume- 

 rous lymphatic vessels of considerable size. They not uncom- 

 monly surround the arteries which they accompany, as 

 represented in fig. 1, and even completely invaginate them, 

 so as to represent " perivascular lymphatics." These vessels 

 are in direct communication with the network of lymphatics 

 already described on the surface of the organ. They are 



