GLANDIFORM BODIES CONNECTED WITH RESPIRATORY APPARATUS. 555 



It is certainly relatively larger in the foetus and young animals than in adults ; 

 but the difference is not sufficiently marked to authorize us in drawing any 

 physiological inductions therefrom. 



2. Thymus Gland (Figs. 335, 336). 



The thymus gland is a transitory organ, being only present in the foetus and 

 very young animals, and in its nature closely resembles the thyroid gland. Like it, 

 it is divided into two lateral lobes, placed close together in the middle line, under 



Fig. 336. 



Fig. 335. 



PORTION OF THYMUS GLAND 

 OF CALF, UNFOLDED. 



a, Main canal ; h, 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 



the lower face of the trachea, partly without and partly within the chest, between 

 the two layers of the anterior mediastinum. It is elongated from before to 

 behind, of a whitish' colour, and uneven or lobulated on its surface like a salivary 

 gland. 



Structure. — It owes its uneven aspect to its lobular structure ; for it is 

 effectively reduced by dissection into a multitude of granular lobules, in the 

 centre of which are found vesicular cavities containing a lactescent fluid. The 

 vesicles are larger than those of the thyroid gland, and have for walls a very 



