158 JEREMIAH S. FERGUSON 



coraco-mandibularis muscle is relatively very broad and com- 

 pletely hides the thj^roid gland ; the gland is described as reniform 

 and voluminous. With the exceptions recorded the position of 

 the thyroid in the various species of Selachii corresponds fairly 

 well with that described for Scyllium. 



Of the Batoidei, in Raia alba the coraco-hyoidei are small and 

 widely separated, and between these muscles the first pair of 

 branchial arteries emerge. The thyroid gland is described as lying 

 between the bifurcation of the aorta and the hyoid arch; it is a 

 very large globular organ and its deeper surface is slightly pro- 

 longed as far as the arterial bifurcation. In Raia oxyrhynchus 

 the thyroid gland in transversely elongated. In Raia pastinaca 

 the coraco-hyoidei approach one another and the gland is longi- 

 tudinally elongated ; in this particular it corresponds to the Sela- 

 chian type. In this last species it is a large pyriform organ with 

 its broad end in relation with the hyoid cartilage, and its point 

 extending nearly to the bifurcation of the branchial artery; at 

 its point the gland presents a prolongation "which descends 

 between the branchial sacs to a depth of about 0.5 cm." I desire 

 to call attention to the fact that in Carcharias a posterior prolonga- 

 tion apparently also exists and is constantly present, but so far as 

 I am able to observe it consists solely of connective tissue and con- 

 tains no glandular substance; it can not, therefore, be in any way 

 analogous to the anterior prolongation of the processus pyrami- 

 dalis. I think it is to be connected with the fascia of the thyroid 

 sinus, which will be discussed later on, rather than with the gland 

 itself. 



Guiard sums up his work on the morphology of the thyroid 

 gland in the rays by saying that the organ lies beneath the coraco- 

 mandibularis, between the coraco-hyoids, is always globous, of 

 more of less pyramidal form, and with a prolongation backward 

 to the bifurcation of the ''branchial artery." This corresponds 

 very well with the condition which I find in Raia Erinacea except 

 that in this species, at least, the gland constantly overlies the bifur- 

 cation of the ventral aorta (branchial artery), and that it is always 

 somewhat flattened, its ventro-dorsal axis being shortened. The 

 organ is relatively thicker than in the Selachians because of the 



