106 



tube. This tube is considered to be a vestigial structure, and must 

 be regarded as the remnant of thyroid duct. Its intimate connection 

 with the thyroid gland, and its direct communication with the mouth, 

 strongly support this conclusion. 



2. Scyllium catulus and Scyllium canicula. 

 I have been led to investigate the relations of the thyroid gland 

 to the basihyal cartilage in the above named species from the fact 

 that, in the figure which Gegenbaur^) gives of the branchial arches 

 of the first named, there is shown a small foramen in the basihyal 

 cartilage corresponding almost exactly in position with that which I 

 have found in Chlamydoselachus. 



In the case of Scyllium canicula I noticed, in examples of the 

 branchial arches which were being prepared for class purposes, that 

 a small foramen was present in all the basihyal cartilages, also cor- 

 responding in position with that in Chlamydoselachus. 



Before proceeding further I may say that in all the figures which 

 I have seen of the branchial arches of this commonly dissected species 



there is no indication of the 

 foramen just mentioned. 



Three specimens of S. 

 catulus have been examined 

 and the foramen figured by 

 Gegenbaue has been found 

 in all of them. About thirty 

 examples of S. canicula 

 have been examined and 

 the foramen, here recorded 

 for the first time, has been 

 found in all. 



I propose to give now 

 a short account of the re- 

 lations of the thyroid gland 

 and the foramen as they occur in S. canicula, because the conditions 

 in this species and in S. catulus are very similar, and more particularly 

 because the foramen in S. canicula has apparently never been de- 

 scribed before. 



In fresh specimens the thyroid gland is found with its investment 

 of soft connective tissue lying between the lateral portions of the 



Fig. 3. Ventral view of jaws and basihyal 

 cartilage of Scyllium canicula. 7io °^t- s'^^- ^^'• 

 basihyal. crh. ceratohyal. /. foramen, m. mandible. 

 pq. palatoquadrate cartilage. 



1) Unters, vergl. Anat. d. Wirbelt., Bd. 3, 1872, Taf. 18. 



