Chap. V. | 



ARTERIAL ARCHES. 



205 



2. Sufoclaviaii. This is given off from the aortic 

 arch, and supplies the fore-limb of either side. 



3. Pulmonary artery (see Fig. 88), which 

 supplies the lungs ; this in the Amphibia, where 



..b 



Fig 89. Diagrams to show the Metamorphosis of the Arterial Arches. 



A, Lizard ; B, Snake ; c, Bird ; D, Mammal. The five primitive arches are shown 

 from below. The first and second arches are always obliterated and their 

 trunks carried on as the internal () and external (6) carotids. These are both 

 continuous with the third arch (c) which forms the common carotid, and in 

 A arises directly from the arterial trunk; in A also the outer trunk between 

 the third and fourth arch persists as the ductus Botalli (d) ; in A and B the 

 two arches of the fourth series are seen to be subequal, to cross one another 

 just outside the heart, and to unite behind it into a dorsal aorta (<j) < in c the 

 left fourth arch becomes the subclavian artery, and takes no part in forming 

 the dorsal aorta; in D the same happens to the fourth arch on the ripht side. 

 In all the primitive fifth arch supplies the lungs, but in mammals the right 

 kalf disappears. (After Rathke.) 



respiration is largely cutaneous (see page 326), gives off 

 a large cutaneous branch, which is distributed in 

 the skin. 



