THE ANATOMY OF THE THYROID GLAND 161 



(4) by the lateral veins and the prolongation of the cardinal 

 sinus into which they open." 



I would like to direct attention to the presence of similar venous 

 anastomoses in the Selachii as well as in the Batoidei. These 

 anastomoses in the cervical region are frequent and voluminous. 

 A complete circular anastomosis surroundsthe mouth close to the 

 maxillary and mandibular cartilages. Though not so readily seen in 

 the Selachii, it follows the same course as in the skate in which fish 

 it is visible through the skin and oral mucosa; it ends in a maxillary 

 sinus at either angle of the mouth, which is connected with the 

 orbital sinus and with the jugular vein. The hyoid sinuses are simi- 

 larly connected across the median line near the ventral surface, 

 two anastomotic vessels, the anterior the larger, connecting the 

 opposite sides. This anastomosis bears a most important relation 

 to the thyroid gland. The anterior vessel is so large as frequently 

 to almost envelop the gland as in a capsule, the vessel is sub- 

 divided by fibrous partitions, or consists, rather, of a mass or 

 series of vessels within a common sheath, and from its relation to 

 the thyroid gland, in its more or less dilated condition it is more 

 truly a sinus than a vein ; it is conveniently designated the thyroid 

 sinus. It fills and empties with each movement of the mouth and 

 gills as water is forced through the branchial clefts, thus function- 

 ing with the aid of extrinsic muscles after the manner of a venous 

 heart. When the fish is examined out of t)ie water the violent 

 movement of the gills so distends the sinus as often to wholly 

 obscure the thyroid gland by the volume of its contained blood. 

 It is almost impossible to reach the gland by dissection from the 

 ventral surface without cutting the sinus or some of its numerous 

 tributaries. The thyroid sinus receives the veins from the thyroid 

 gland, most of these vessels leaving the dorsal surface or posterior 

 margin of the organ. 



T. J. Parker ('86) offers a description of the larger blood-vessels 

 of Mustelusantarcticus, which is, however, deficient as regards the 

 ultimate distribution of the smaller arteries. Exceptions may also 

 be taken to his statement of the distribution of the arteries which 

 constitute the rather remarkable hypobranchial arterial system, 

 which as already mentioned, bears an important relation to the thy- 

 roid gland. Parker's description of the venous system is quite 



