A glycogen body is an oval structure in the spinal cord of birds that is made of specialized cells that contain large amounts of glycogen. Housed within the synsacrum, the function of this structure is not known, but it does not seem to be related to the normal function of glycogen in animals, which is the storage of energy.

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Various theories have been put forward to explain its function :

• it may assist in myelin formation (for nerve fibres) (source)
• it might control water and sugar levels in the central nervous system (source)
• alternatively, it could be 'metabolically inert', i.e. has no function.