650 FRANCIS M. BALDWIN 



section at this stage, (fig. 35) the epithelial body (e.b.2) lies just 

 lateral to the point where the second aortic arch bends dorsally 

 to join the dorsal aorta and is a little below the level of the 

 branchial cartilage (1). 



The structures are exposed by gross dissection in fully adult 

 animals (e.6.1,2, fig. 40), by removing the skin and superficial 

 muscles from the neck region. They lie in the connective tissue 

 medial to the distal tip of the first branchial cartilage. The 

 carotid gland (e.g.) is a very evident oval body of small size, into 

 which the first afferent branchial artery enters, and from which 

 the external and internal carotid arteries pass forward. Close 

 behind and a little lateral to it, are the two small, whitish, or 

 yellowish white epithelial bodies. These are slightly oval, nearly 

 equal in size (varying from 200 to 300 micra in diameter) ; they 

 lie one closely behind the other and are enveloped in connective 

 tissue which contains considerable pigment. By carefully dis- 

 secting and clearing the parts, it is evident that the blood supply 

 of this region is by two small arteries, one passing back from the 

 second aortic arch, and the other from the external carotid artery. 

 I was unable to trace the origin of numerous small nerve twigs, 

 but it is probable that the region is innervated by branches (prob- 

 ably the third and fourth) of the vagus nerve. 



There is little histological difference between the adult epithelial 

 body and that of the late transforming stage. The epithelial cells 

 are solidly packed, separated only .by a very fine matrix, the 

 whole surrounded by a well marked layer of connective tissue. 

 Such a compact condition differs slightly from the structure of the 

 body in Triton and Salamandra where (Maurer) they were com- 

 posed of irregular masses of epithelial cells separated one from 

 another by strands of connective tissue. 



III. REVIEW OF THE LITERATURE 



A considerable literature deals with the structures derived from 

 the pharyngeal wall and gill-pouches of the amphibians, and, since 

 various authors have described identical structures in the same 

 species and homologous ones in related forms under different 

 names, the results are sometimes confusing. 



