The axons of myelinated neurons are embedded in a protective covering of

Myelin sheath

Explanation:

Myelin sheath is a protective covering in axons that consist of lipids and proteins, produced by oligodendrocytes. This covering protects the nerve cells from receiving any other electrical impulses not directed to them. It also effeciently speeds the transmission of nerve messages amongst nerve cells in the nervous system.

what's the question?

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