240 CHARACTERS OF VERTEBRATE ANIMALS 



There are not many points which need detain us in the 

 structure of the digestive organs (fig. 150). A considerable 

 number of small teeth, with forked crowns, are fused with the 

 bones which form the margins of the jaws, and there are two 

 longitudinal rows of similar teeth on the roof of the mouth. 

 Gullet, stomach, small intestine, and large intestine are present, 

 the last being very short and opening behind into a cloacal 

 chamber. The Salamander is found in damp places, where it 

 lurks in crevices, coming out in the evening or during rain to 

 feed upon worms, snails, and slugs. 



Very special interest attaches to the circulatory organs (fig. 

 150), especially as regards the structure of the heart and the 

 arrangement of the large arteries. There is a certain agree- 

 ment with the Sand Lizard (see p. 191) in so far that the great 

 veins open into a thin-walled venous sinus, that pours the impure 

 blood it receives from them into a right auricle, which is separated 

 by a party-wall from a left auricle receiving pure blood from the 

 lungs. Both auricles open into the single ventricle. But there 

 is here not even an internally projecting ridge for partial division 

 of the ventricle into right and left halves, and there is an additional 

 region to the heart, the arterial cone, a tube which is in communi- 

 cation with the cavity of the ventricle on the right-hand side, and 

 from which the great arteries take origin in the form of four pairs 

 of arterial arches. It is now time to consider more fully the 

 actual meaning of such arches, which have been seen to be 

 present, though in a much less pronounced form, in Reptile, Bird, 

 and Mammal (see p. 201). 



A Salamander when starting an independent existence is 

 unlike the adult in many important respects, and is therefore 

 called a larva. In this particular case, though a pair of small 

 lungs are present, they are, to begin with, of little or no use for 

 breathing purposes. The efficient organs of respiration are three 

 pairs of feathery gills growing from the sides of the throat, and 

 containing a net-work of delicate blood-vessels. Floating freely 

 in the surrounding water, these gills present a large surface 

 through which the dissolved oxygen can diffuse into the blood 

 and the waste carbon dioxide diffuse out of it. Close inspection 

 reveals the presence of four small gill-slits on each side of the 

 throat, by which the back part of the mouth-cavity communi- 

 cates with the exterior, and each slit is in front of a corresponding 



