THE DIGESTIVE AND RESPIRATORY SYSTEM 309 



the moist, glandular skin becomes an effective respiratory 

 organ. 



The pharyngo-cesophageal system appears to be a special 

 compensation for the loss of the lungs, and is present in only 

 those salamanders in which the pulmonary system has been 

 lost (Fig. 86). Here again the incentive towards the for- 

 mation is a moist membrane richly supplied with capillaries, 



Oesopliageal 

 Muscle 



Art.Pharyngea 



Portion of 

 PulnaonaryArck 



\anasiomoses 

 here with the 



Art.Gastrica 

 V. aesophagea 



FIG. 86. Pharyngo-cesophageal lung of Desmognathus, showing pha- 

 ryngeal and oesophageal muscles, and the net-work of blood-vessels in the 

 walls of the pharynx and oesophagus. 



in this case, the mucous lining of the pharynx and oesophagus. 

 The natural vascularity of this structure has been considerably 

 increased, while the capillaries themselves have become more 

 superficial and even invade the external epithelial layer, the 

 only case known. The muscles of the lost pulmonary system 

 have been in part retained, and through their aid, together with 

 that of others which are developed for that purpose, the 



