286 SANTE NACCARATI 



the right than on the left; when the animal's neck is extended, the 

 point of bifurcation of the two carotid arteries and the right 

 subclavian is in a line with the right forepaw. 



In connection with the thyreoid arteries it must be noted that 

 there are many variations, especially of the superior pair, which 

 often, instead of penetrating the gland directly, join the inferior 

 pair, thus entering the gland as a single trunk. When this occurs, 

 the superior thyreoid artery turns downward immediately after 

 leaving the carotid and follows a course of about 1 cm., while 

 the inferior artery, turning sUghtly upward, follows a very short 

 course. The trunk which results from their union is so short 

 and thick that it resembles an arterial sinus. 



At other times the superior thyreoid artery is missing, and is 

 replaced by three or four small arteries forming a network around 

 the upper tip of the gland. At still other times there may be 

 a median artery which arises from one of the two carotids near 

 the hyoid bone and turns downward along the median line of the 

 neck, reaching the upper tip of the gland. 



The ramifications of these arteries, finely divided, form a 

 plexus around the fibrous capsule which surrounds the gland, 

 and penetrate the parenchjana, where they form a very fine 

 capillary network interwoven with the thyreoid vesicles, which 

 they enclose, passing through the intervesicular septa. The 

 musculature of these vessels is very distinct. 



The veins which originate in the form of fine branchlets 

 traversing the vesicles compose on the surface of the gland a 

 thick venous network, a large plexus from which issue the princi- 

 pal veins (inferior thyreoid) ; the latter unite with the accessory 

 pectoral veins and empty into the subclavian vein formed by the 

 confluence of the jugular and axillary veins. 



The fine perivesicular veins are without musculature and ap- 

 pear as Uttle tubes with endothelium alone, traversing the inter- 

 lobular connective tissue. Fine elastic' fibers passing through 

 this tissue seem to provide a kind of support for the larger 

 vessels. The lymphatics are also very numerous; as in human 

 thyreoid, they arise as small vacuoles between the cells lining the 

 vesicles; these unite to form intervesicular canals, and those in 



