PHARYNGEAL DERIVATIVES OF AMBLYSTOMA 669 



pericardium, and, in the adult, it is flanked medially by the genio- 

 hyoideus, laterally by the hyoideus internus muscle of the first 

 branchial arch, and dorsally by the sternohyoideus muscles. 



16. From the condition of the follicles in the late transforming 

 and early adult gland, it is evident that new and smaller follicles 

 are being budded from the larger ones. 



17. The blood supply of the adult gland is from small venous 

 twigs coming from either the sternohyoideus or geniohyoideus 

 muscles (never from the large inferior jugular trunk). These,, 

 upon entering the gland, break up into numerous smaller vessels 

 Crete mirabile') and join the jugular vein some distance caudad. 

 A connection with the external carotid artery is very doubtful, 

 in only a single case did a small twig (probably the thyreoid 

 artery) pass into the vascular network of the gland. 



18. The anlage of the postbranchial body is recognized in larvae 

 8 mm. long. It develops as a rule on the left side (in single 

 individual, 19 mm. long, on the right side as well). At first it is a 

 thickening of a portion of the pharyngeal floor, between the 

 anlage of the fourth branchial (fifth visceral) pouch and the an- 

 lage of the glottis, and protruding slightly ventrally toward the 

 dol-sal wall of the pericardium. It is thus 'postbranchial' as 

 Maurer claimed for the similar structure in Triton, and appears in 

 the relative position of the sixth pouch. 



19. In 9.5 mm. larvae, the anlage makes a solid cylindrical 

 stalk of cells extending vertically downward from the floor of the 

 pharynx. It soon elongates, loses its connection with the pharynx 

 and as a irregular, poorly defined mass of cells extending in an 

 anterio-posterior direction lies medial to the aditus laryngeus 

 muscle. 



20. In one 19 mm. larva, a postbranchial body was found on the 

 right as well as on the left side; the left being the larger. This 

 unusual condition is of interest since it shows variability within 

 a genus of urodeles. It is also important as bearing upon the 

 questions of homologies of these structures. 



21. In the later larv^al stages the postbranchial body becomes 

 very irregular; in some regions it is solid, in other parts it shows 

 follicular structure, with cuboidal cells forming a fairly definite 



JOURNAL OF MORPHOLOGY, VOL. 30, NO. 2 



