THYREOID GLAND OF THE TELEOSTS 



765 



SARDA SARDA BLOCK 



Length of specimen 50 cm. The thyreoid gland of the Spanish 

 mackerel shows the most remarkable conditions of all fish thyreoids. 



The mass of the organ is enormously large and the dorso-ventral 

 and cephalo-caudad extensions are unusual. The relation of the 

 thyreoid gland to other tissue is singular, and could be compared 

 only with that in Brevoortia. There exists such an intermingling 

 of thyreoid, bone, cartilage, smooth and striated muscle fibres, 

 fat and connective tissue that it is impossible sharply to define 



Fig. 11. Sections through the thyreoid gland of Mugil. A, anterior to; B, at 

 the aortic bifurcation; C, near the second branchial arteries. 



