In early development, as the nerve cord is forming, neural crest cells leave the nerve cord and move through the body. These cells form, or cause to form, many important nerves, neural ganglia, and many head and facial features. Vertebrates possess two types of bone. Vertebrae, ribs, appendages, and the jaw are endoskeletal bone. The vertebrate skull is actually a complex structure of both endoskeletal and dermal bone.
All vertebrates have cartilage in addition to bone, or instead of bone.
Romer, A. S. and Parsons, T. S. 1986. The Vertebrate Body . Saunders College Publishing, Philadelphia.