TRITON 95 



vertebrates, where it gives rise to the allantois. For this reason 

 the bladder of Amphibia is called " allantoic," to distinguish 

 it from the swellings of the urinary ducts or " bladders " of 

 fish. The liver is divided into several lobes, a gall-bladder is 

 present and the bile-duct which leads from it joins the duct 

 from the pancreas to open into the intestine. 



Respiratory and Vascular Systems. — The windpipe, or 

 trachea, leads back ventral to the gut and divides into the two 

 bronchi leading to the lungs. These differ from the lung of 

 Ceratodus only in that they are paired, and that they maintain 

 their primitive position ventral and lateral to the gut. In the 

 adult the gill-slits have disappeared, and the afferent and 

 efferent branchial arteries are directly continuous instead of 

 being separated by the capillaries of the gills. These arteries 

 are now called arterial arches, and they run round the pharynx 

 from the ventral to the dorsal side as if they were still separated 

 from one another by the gill-slits. The ventral aorta is shortened 

 up so much that the arterial arches come off from the truncus 

 arteriosus, close to the heart. The ist arterial arch runs in the 

 mandibular arch, and the 2nd arterial arch likewise ascends the 

 hyoid arch. Although present in the embryo, these arterial 

 arches disappear. The 3rd arch persists as the carotid. At 

 its base is the lingual artery which represents the anterior 

 prolongation of the original ventral aorta. The carotid then 

 passes through the carotid gland (see p. 401) and ascends the 

 3rd visceral (ist branchial) arch until it reaches a position 

 dorsal to the pharynx. Here it turns forwards and enters the 

 skull. It is the anterior prolongation of the original dorsal 

 aorta. 



The 4th arterial arch is known as the systemic. It goes 

 up in what was the 4th visceral (2nd branchial) arch and turns 

 backwards. Arrived here, dorsal to the pharynx, this vessel 

 is exactly in the position of and corresponds to the lateral 

 dorsal aorta of fish, only it has lost its connexion with its 

 anterior prolongation which is now the internal carotid. This 

 connexion, when present, is called the ductus caroticus. 



The 5th arterial arch disappears in Triton, though it is 

 present in the nearly related form Salamandra, where it leads 



