474 



THE RESPIRATORY APPARATUS. 



externally by an almost amorphous membrane which divides it into " acini," 

 or gland-granules. Separate acini are often observed on the main canal. 

 Each lobule is made up of its greyish-white, soft parenchyma composed of 

 free nuclei and small cells, and has a minutely-distributed capillary plexus* 



Fig. 245. 



Fig. 244. 



PORTION OF THYMUS 

 GLAND OF CALF, 

 UNFOLDED. 



a, Main canal ; 6, 

 Glandular lobules ; 

 c, Isolated gland 

 granules seated on 

 the main canal. 



COURSE AND TERMINATION OF THE ABSORBENT 

 DUCTS OF THE THYMUS GLAND OF A CALF. 



1, Internal jugular veins ; 2, Superior vena cava; 

 3, Thoracic duct, dividing into two branches, 

 that again unite before terminating in the root 

 of the left jugular vein ; 4, The two thymic 

 ducts : that on the left side opening into the 

 thoracic duct, and the right into the root of 

 the corresponding jugular vein. 



The lymphatics terminate in two large ducts that commence at the upper 

 extremities of the lobes of the gland, the thymic ducts, and pass down- 

 ward to terminate at the junction of the jugular and axillary veins at each 

 side.) 



DIFFERENTIAL CHARACTERS IN THE GLANDIFORM BODIES ANNEXED TO THE RESPIRATORY 

 APPARATUS IN OTHER THAN SOLIPED ANIMALS. 



The thyroid body, peculiar to Mammals, is more developed in Ruminants, Pachy- 

 derms, and the Carnivora, than in Solipeds. The two lobes are closer together, and 

 often joined by the thyroid isthmus. In the Pig this is very marked, and the gland 

 well merits its name, as it forms a veritable shield in front of the trachea, towards the 

 lower part of the neck. 



