THYREOID GLAND OF THE TELEOSTS 717 



importance. The thyreoid does not receive its blood supply from 

 this group of vessels, since they carry only venous blood, and the 

 arterial blood which nourishes the gland comes from a special 

 thyreoid artery. In Petromyzour however, Cori claims that the 

 arteria thyreoidea arises from the truncus arteriosus ; this is prob- 

 ably an error, as he also finds the ventral carotid connected with 

 the truncus. The thyreoid artery, as Silvester demonstrated in 

 Lopholatilus and twenty other species of Teleosts by his perfected 

 method of injection, arises as a dorsal branch from the united 

 right and left fourth commissural arteries. The latter vessels 

 originate from the second efferent branchial arteries and unite in 

 the median line below the thyreoid and the aorta as the hypo- 

 branchial artery. Shortly after the union of the fourth commis- 

 sural arteries the thyreoid artery branches off from the dorsal 

 side and immediately enters the gland in its posterior region. 

 Whether the widely scattered follicles all receive their capillaries 

 from this one vessel cannot at present be stated, though it would 

 seem very doubtful especially in the case of the more anteriorly 

 isolated follicles. 



In Selachians, where the thyreoid is pushed far forward, the 

 arteria thyreo-spiracularis (Dohrn) originates in the first aortic 

 arch from the arteriae efferentes of the hyoid gill. In Teleosts, 

 also, the first aortic arch breaks up into a capillary network. 

 Dohrn, therefore, speaks of an arteria thyreo-spiracularis. Per- 

 haps it is from this vessel that the most cephalad parts of the 

 thyreoid gland receive their blood supply. The artery pointed 

 out by Silvester seems, however, to supply the bulk of the organ, 

 and the term arteria thyreoidea as applied to it is apparentl}^ 

 justified. 



It is of interest to recall Simon's statement, which was also 

 supported by others, that the thyreoid gland is placed in the blood 

 system so as to regulate the supply of blood to the brain. This, 

 in a way, was a foreshadowing of our present views that the phy- 

 siological action of the thyreoid gland exerts an important influence 

 on the central nervous system. 



The venous blood from the thyreoid gland passes into the thy- 

 reoid vein, a vessel, which also collects the veins from the muscula- 



