ENDOCRINE SYSTEM OF TYPHLOMOLGE RATHBUNI. 



305 



In addition to the main portions of the thyroid, most specimens 

 possess accessory thyroids. These develop from small cell 

 groups which during migration become detached from the main 

 portions and thus mark the path along which the main portions 



In reproduction figures i to 8 have been reduced by one third, figures 9 and 10 by 



slightly more than one third. 



FIG. i. Location of main portion of right thyroid in an advanced larva (59.2 

 mm. total length) of Ambystoma opacum; I, first gill arch; B, first basibranchial; 

 H, hyoid; L, lymph space; M, cavity of mouth; O, operculum; P, pericard; T, 

 thyroid; V, anterior cardinal vein. 



migrate. Their location varies greatly. They are located usually 

 anterior and may be either ventral or dorsal or, in case of several 

 accessories, both ventral and dorsal to the main portions. Or 

 they may be at one level with the main portions. They consist 

 either of one or several median rudiments located in the median 

 interstitium of the muscles ventral to the basibranchials of the 

 visceral skeleton (genio-hyoideus) or of two lateral portions, one 

 on each side, which either are attached to the sides of the basi- 

 branchials or are located in the interstitia of the muscles lateral 

 and ventral to the basibranchials. In some Ambystomidae 



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