<P> All extant cephalopods have a two - part beak, or rostrum, situated in the buccal mass and surrounded by the muscular head appendages . The dorsal (upper) mandible fits into the ventral (lower) mandible and together they function in a scissor - like fashion . Composed primarily of chitin and cross-linked proteins, beaks are more - or-less indigestible and are often the only identifiable cephalopod remains found in the stomachs of predatory species such as sperm whales . They can be used to estimate the mantle length and total body weight of the original animal as well as the total ingested biomass of the species . Cephalopod beaks gradually become less stiff as one moves from the tip to the base, a gradient that results from differing chemical composition . In hydrated beaks of the Humboldt squid (Dosidicus gigas) this stiffness gradient spans two orders of magnitude . </P> <P> Fossilised remains of beaks are known from a number of cephalopod groups, both extant and extinct, including squids, octopuses, belemnites, and vampyromorphs . Aptychi--paired plate - like structures found in ammonites--may also have been jaw elements . </P> <P> The beak may also be referred to as the mandibles or jaws . </P> <Table> <Tr> <Td> <Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> Side view of the lower beak of Chiroteuthis picteti (3.6 mm LRL, 160 mm ML (estimate)) 3D red cyan glasses are recommended to view this image correctly . </Td> </Tr> </Table> <Table> <Tr> <Td> </Td> </Tr> <Tr> <Td> Side view of the upper beak from the same specimen (2.7 mm URL) </Td> </Tr> </Table> </Td> </Tr> </Table>

Where is the beak of a squid located