154 JEREMIAH S. FERGUSON 



would appear to be not very accurately expressed, for it never 

 arises from the afferent branchial vessel which leaves the dorsal 

 end of the branchial arch, but, on the contrary, arises from the 

 ventral end of the nutrient or efferent loop. The relation of the 

 thyroid gland to the bifurcation of the ventral aorta is so intimate 

 as to readil}^ suggest the error of other observers who have pre- 

 sumed that the organ received some blood directly from the first 

 pair of branchial arteries. Moreover, the thyroid artery passing 

 from its origin lies directly under, and in contact with the first 

 pair of afferent branchial arteries so that until these latter vessels 

 have been carefully dissected out of their sheath it is impossible 

 to determine with certainty that they have no connection with the 

 thyroid vessels. In the skate the gland lies directly upon the aor- 

 tic bifurcation and the pulsating blood-vessels are readily seen 

 through the transparent organ as soon as it is exposed. 



Miiller ('71) speaks of the thyroid gland of Raia clavata as a 

 flattened brownish-red body, lying at the point of division of the 

 branchial artery. It possesses a connective tissue capsule with 

 trabecula which divide the organ into a small number of lobes, 

 within which the connective tissue penetrates between the lobules. 

 The follicles possess a thin membrana propria and a cylindrical 

 epithelium; they contain a homogeneous, gelatinous yellowish 

 mass. The epithelium possesses a shiny cuticular border and 

 appears to send processes into the lumen. The description given 

 by Miiller holds good for Raia, the genus which he studied, but 

 it does not correspond to the condition of the thyroid gland of 

 Mustelus, Squalus or Carcharias, the difference being chiefly due 

 to the fact that in the Batoidei the connective tissue forming the 

 thyroid trabecula and interfollicular septa is apparently much 

 more abundant than in the Selachii. 



Balfour ('78) discusses very briefly the early development of the 

 thyroid gland of Elasmobranchs prior to the appearance of a 

 lumen within its follicles. He does not consider the anatomy of the 

 organ in the adult. 



Baber ('81) says that ''in the skate the gland is single (with the 

 exception of a few detached vesicles) and forms a j^ellow, flattened, 

 lobulated body, occupying the median line at the bifurcation of 



