The skeleton of a shark is mostly made of cartilage, which is present in a similar state in the skeletons of other animals. Some parts of the skeleton may calcify to reinforce points of mechanical stress, but it is still a cartilaginous skeleton

The cranium is a block of compact cartilage encircling the brain, olfactory and auditory capsules. Lateral cavities protect the eyes. Some cartilage skulls project anteriorly to form a rostrum at the front of the head. Jaws, which are made of bone, are attached loosely to the botom of the skull as well as being connected by a short rod of cartilage in front of the gill arches. Details of this attachment aid researchers of shark evolution. Gill arches are cartilage rods hooping around the body ontours. Most sharks have five gill slits to aid the gill arches in respiration, and a few have six or seven.

Each section of the vertebral column - or vertebra - has a centrum with an arch to protect the spinal cord. They have no ribcage, but have processes from each centrum that represent a modified sort of rib. Their spine goes almost to the end of the upper half of their tail, or caudal fin. The other fins are supported by cartilaginous spines. Pectoral fins are secured to the spine by a thick pectoral girdle. The pelvic girdle lies unsupported within the ventral muscle layers for easier maneuverability.

A shark's mouth is quite literally stuffed with teeth that have an enamelled blade and one or more cusps. Commonly, they have a large middle cusp with a small cusp on each side. This is a valueable marker for species identification, as well as the position of the tooth in the jaw. Teeth are replaced throughout the shark's life. Teeth form behind the cartilage of the jaw and move to the front in assembly line fashion as the old ones fall out. Only a very few sharks have teeth developed for grinding. Most merely bite off chunks of meat from their victims and swallow whatever they got whole. In several sharks the male's teeth are larger that those of the female. This is thought to prove that males bite females to hold on during mating.