THE ANATOMY OF THE THYROID GLAND OF ELAS- 

 MOBRANCHS, WITH REMARKS UPON THE HYPO- 

 BRANCHIAL CIRCULATION IN THESE FISHES 



JEREMIAH S. FERGUSON 

 Assista7it Professor of Histology, Cornell University Medical College 



TWENTY FIGURES 



Introduction •. . 151 



Review of the literature 163 



Material and methods 164 



The anatomical relations of the thyroid gland 165 



The thj^roid vessels 171 



The hypobranchial circulation and the origin of the thyroid vessels 175 



Veins and lymphatics of the thyroid region 183 



The histology of the Elasmobranch thyroid gland 187 



Summary 207 



Explanation of figures 209 



Bibliography 210 



INTRODUCTION 



Even a casual reference to the literature of the thyroid gland is 

 sufficient to indicate that the organ has been more carefully stud- 

 ied in most all other classes of animals than in the Elasmobranchs. 



The organ may be said to make its first appearance in the As- 

 cidians, Amphioxus, and Cyclostomes as a depressed groove, trough, 

 or series of recesses in the ventral fioor of the pharynx, usually 

 known as the endostyle, or the hypobranchial or hypopharyn- 

 geal groove, which, as first shown by W. Miiller ('71) who studied 

 Myxine glutii;iosa and Petromyzon, is to be considered the homo- 

 logue of the median thyroid of the vertebrates. In the Cyclo- 

 stomes the structure, relations and development of the primitive 

 thyroid have been more recently studied bj^ Guiard ('96), Cole 

 ('05), Schaffer ('06), and Stockard ('06). The structure of the 

 organ is very simple and only partially resembles the thyroid of 



