AMPHIBIA 207 



in the right lobe, is connected with the gall bladder by a cystic 

 duct, and receives tributary ducts from the left lobe. As it 

 runs down the mesentery between the duodenum and stomach, 

 it passes through the pancreas and receives from the pancreas 

 the pancreatic duct. In the lower part of its course the duct 

 is therefore a pancreatic-bile duct, and this opens into the 

 duodenum. The pancreas is the triangular yellow patch 

 which occupies so large a portion o the mesentery, connecting 

 the duodenum with the stomach. The digestive processes 

 are very similar to those of the higher Craniata. 



The respiratory organs of the adults are a pair of lungs 

 which arise as paired outgrowths of the oesophageal wall. 

 These meet to form the single opening, the glottis. The 

 glottis opens into a larynx, and the larynx is supported by 

 arytenoid cartilages developed with constrictor and dilator 

 muscles from splanchnic mesoderm, 1 and the inner layer is 

 reflected to form vocal cords. Frogs are silent usually, except 

 in the breeding season, when croaking is indulged in. The 

 lungs spring at once from the tube immediately below the 

 larynx, and are delicate sacs lying one on each side of the 

 oesophagus. The walls are protruded into shallow air sacs, 

 and the thin epithelium of the air sacs and of the network of 

 capillaries brings the blood into intimate relationship with 

 the air. Breathing is accomplished by the floor of the mouth 

 being depressed, with the result that air is drawn into the 

 mouth cavity through the nasal passages. The valve in 

 the nostril is closed and the air is driven into the lungs by the 

 raising of the floor of the mouth. The respiratory pigment is 

 haemoglobin, as in other Craniates. 



The skin is also used for respiration, and when the animal 

 is submerged is necessarily the organ of breathing. 



Coelom. The coelomic mesoderm is resolved into dorsal 

 myocoels and the ventral splanchnocoel. The myocoels are 

 segmented, and after they are separated from the splanchno- 

 coel they lose their cavity and grow downwards. Their inner 

 cells form the skeletal musculature and buds are developed 

 from them to the limbs, and their outer layer is converted 

 into the dermis. With the loss of the tail the primitive 

 1 1920. Edgeworth, Jour, of Anat. vol. 54. 



