490 Ealpb 11. Major. 



The next vascular unit which comes into consideration is what 

 might be termed the lobar unit, and is formed by the arteries of 

 the second order, which surround collections of lobules or lobes and 

 give oif arteries of the third order. The corresponding structural 

 unit is not so easily determined as are the lobules, but they may be 

 considered as a collection of lobules, which is marked off from 

 a similar collection of lobules by denser septa. The term lobe as 

 used here is the microscopic lobe and does not refer to the lobe of 

 gross anatomy, the term which is applied to a much larger anatom- 

 ical division of the gland, for in the human the gland is considered 

 as composed of a median and two lateral lobes, and in the dog 

 the term lobe is applied to what is really gross-anatomically considered 

 a right and a left thyroid gland. 



As arteries of the first order, for the sake of simplicity, have been 

 grouped together, the branches of the thyroid arteries which ramify 

 over the surface of the gland, supply definite regions and penetrate 

 it giving off branches of the second order. 



Finally as the largest unit present, the prime unit, we have the 

 thyroid gland itself, supplied by the thyroid arteries, superior and 

 inferior, which diftVrentiate it from the standpoint of vascularization 

 from surrounding structures such as the thymus, submaxillary gland, 

 etc. 



An exhaustive study of the lymphatics of the thyroid does not 

 lie in the scope of these notes. Many observers, among them Baber 

 (5) and more recently Renaut and Petijean (16), have described 

 them and most of the text-books refer to their presence, their extreme 

 richness and their general distribution. Yet a short consideration 

 of their relation to the blood vessels may be of interest. The lymph 

 spaces surround each follicle just outside the capillary network, 

 filling in as it does the interstices left between the follicles. The 

 relation between the capillaries and the lymphatics also indicates how 

 the individual follicles are surrounded by lymphatic spaces. These 

 spaces connect with larger trunks which definitely run in between the 

 different lobules. These trunks in turn run into larger ones be- 

 tween the lolx's which follow fairly closely the course of the blood 

 vessels and becoming larger finally unite to form a network of 



