PHARYNGEAL DERIVATIVES OF AMBLYSTOMA 649 



The cartilages of the arches are altered to the hyoid apparatus of 

 the adult; the afferent and efferent branchial arteries now form 

 functional aortic arches; the muscles of the ventral pharyngeal 

 region are greatly enlarged, and as a result, the carotid gland and 

 epithelial bodies are carried somewhat caudal and lateral. 



The carotid gland is now an enlarged, ovate body (489 x 200 

 micra) situated close behind and a little lateral to the caudal end 

 of the thyreoid gland. It is enveloped in a rather heavy con- 

 nective tissue covering. The first afferent branchial artery enters 

 it medially, a little toward the caudal end, while the two carotid 

 arteries leave it anteriorly. 



The first epithelial body is a well defined oval structure (180 

 X 100 micra), composed of closely packed epithelial cells sur- 

 rounded by a conspicuous connective tissue covering, situated 

 close behind (about 150 micra) and a little dorsal to the carotid 

 gland, and just lateral and caudal to the second aortic arch. The 

 second epithelial body is similar to, but somewhat smaller (120 

 X 70 micra) than the first, and lies close behind (between 60 to 

 70 micra) and a Httle lateral to it. The third (very small) aortic 

 arch, passes from the ventral aorta, just in front of the epithelial 

 body, (the epithelial bodies appear in section with the third and 

 fourth thymus bodies, and they lie some distance below them). 



B. Carotid gland and epithelial bodies of adult. These structures 

 present only minor differences from the other stages. In a wax 

 model of the parts, (fig. 42) on the left side, just after metamor- 

 phosis, the carotid gland {e.g.) and epithelial bodies {e.h.) lie close 

 behind one another, imbedded in the connective tissue medial to 

 the first branchial cartilage. The first aortic arch {!) passes 

 slightly caudo-laterally, as it leaves the ventral aorta, and enters 

 the carotid gland as before. The second aortic arch '{2) is large, 

 and, after taking a latero-caudal direction, turns dorsal and 

 cephalad to join the dorsal aorta. The third aortic arch has 

 now disappeared, while the fourth (4) is modified to function as 

 the pulmonary artery {p.a.), a small ductus arteriosus persisting. 

 With these changes in position and function of the blood vessels, 

 the two epithelial bodies are not closely associated, but are more 

 lateral and somewhat more caudal in position. In transverse 



