VERTEBRATES 
69 
fish-like animal called Amphioxus (am-fi-oks'iis), the noto¬ 
chord persists and there is never a true backbone. The 
notochord is always found above the food tube and below 
the spinal cord. 
Another characteristic common to all vertebrates is the 
presence of gill-slits. These are external openings on each 
side of the neck that in the fishes allow the water to pass 
Figure 60. — Sunfish or Pumpkinseed. 
The one usually caught by the small boy fisherman. 
over the gills. Such structures are of use only to aquatic 
animals, and yet all vertebrates have them at some time in 
their development. 
In most vertebrates the skeleton is composed of bone. 
There are usually two pairs of appendages (legs, wings, 
or fins) attached to the body at the shoulder and hip. Here 
special bones join the limb to the body. The bones in the 
shoulder are known as the pectoral (pek'to-ral) girdle ; while 
