The tube that leaves the stomach (and is the first part of the small intestine) is called the

duodenum

Explanation:

duodenum is the first part of the small intestine

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands