638 FRANCIS M. BALDWIN 



been described by a number of investigators (Maurer, '88; 

 Bolau, '99; Driiner, '04; and others) but little is said concerning 

 the morphology of the gland in Amblystoma. Maurer, after 

 describing the development of the gland in Triton remarks, (p. 

 363) "bei Siredon pisciformis findet die Anlage der Schilddriise 

 . . . . in der gleichem Weise bei Triton taeniatus statt," but 

 he says nothing concerning the later larval and adult stages. 

 Although, in the main, the facts of development accord with 

 Maurer's description of both Triton and Siredon, Amblystoma 

 differs in one or two points from either. I therefore give here 

 a brief description of the gland, based for the most part upon the 

 gross dissection of the gland in several adult Amblystomae, 

 chiefly A. tigrinum. 



By removing the skin and caudal portion of the mylohyoideus 

 muscle of the ventral surface of the neck the gland is seen {tr., 

 fig. 36) imbedded in rather loose connective tissue, in front of 

 and a httle lateral to the pericardium, flanked medially by the 

 geniohyoideus, laterally by the hyoideus internus of the first 

 branchial arch, and dorsally by the deeper lying sternohyoideus 

 muscles. It is a rather flattened ovate body (between two and 

 three millimeters long, and from one to two and a half milli- 

 meters broad), differing in shape and size in individuals, and on 

 either side of the same specimen. It is gray or yellowish or even 

 sometimes brownish in color. Usually the cephahc end is pointed 

 and the caudal blunt. Although somewhat variable in their 

 relation to the gland, the blood vessels are very conspicuous. The 

 inferior jugular vein is now large and prominent, and passes 

 lateral to the gland as it courses toward the heart; the external 

 carotid artery parallels it closely as it passes forward from the 

 carotid gland. 



The gland and blood vessels were removed from several in- 

 dividuals and were cleared and mounted. Four glands were thus 

 treated; both right and left glands of A. tigrinum 15 cm. long, 

 and one gland each from other specimens of the same species, 

 17.5 cm. and 22 cm. respectively. The blood supply of the gland 

 is variable. In most cases, the interfollicular net-work of the 

 gland is formed by the small venous twig which passes caudad 



