THE ANATOMY OF THE THYROID GLAND 165 



the blood-vessels injections were made into both remote and near- 

 by vessels, the points selected including the hyoid and thyroid sin- 

 uses, the thyroid artery, the efferent branchial loops and commis- 

 sural arteries, the median hypobranchial artery, the coronary ar- 

 teries, the ventral aorta, conus arteriosus, cardiac ventricle and 

 auricle, the caudal artery and vein, the mesenteric artery and the 

 dorsal aorta. Injections from these various points were made not 

 only because of expediency in a given species but for the special pur- 

 pose of determining the direction of flow and the relation of the 

 vessels to the thyroid circulation; hence, injections were made from 

 both sides of the branchial circulation, in the direction of the flow in 

 the veins and the arteries while other injections were made in a 

 direction opposite to the usual course of the circulation on the 

 arterial side, though this was, of course, impossible in the veins 

 because of the presence of valves. 



Many of the thyroid glands were cleared and mounted in toto. 

 This was best accomplished with those from Mustelus, in which 

 species the gland is very thin. Some of the others were cut free- 

 hand into thick sections. These preparations gave very good 

 pictures of the lymphatics and blood-vessels except in the case of 

 the very thick glands. Still other thyroid glands were sectioned 

 for histological study. 



THE ANATOMICAL RELATIONS OF THE THYROID GLAND» 



The thyroid gland is more or less closely related to most of the 

 structures of the ventral cervical region, a region included between 

 the mandible in front, the coracoid arch or shoulder girdle behind, 

 and the branchial clefts on either side. This region forms the ven- 



1 The fact that the thyroid ghxnd may be readily overlooked in the Selachii 

 is amply demonstrated by the frequency with which this region has been studied 

 and the almost entire absence of any adequate description of the gland. A brief 

 description of the methods of dissection which may be relied upon to locate and 

 expose the gland is offered in the hope that it may materially aid future investi- 

 gation of this organ. 



The thyroid gland of Elasmobranchs can be readily reached from either the 

 oral or the cutaneous surface. By the cutaneous route two methods are especially 

 serviceable, the one by longitudinal, the other by transverse incision. 



THE AMERICAN JODRNAl. OP ANATOMY, VOL. 11, NO. 2 



