Nervous System and Sense Organs

The pigeon's nervous system has a central division (brain and spinal cord), a peripheral division (12 pairs of cranial nerves and 38 pairs of spinal nerves), and an autonomic division (sympathetic and parasympathetic nerves and ganglia supplying the digestive, respiratory, circulatory and urinogenital systems). The brain, short, broad and rounded, sits within the cranial cavity wrapped in two meninges - an outer duramater and an inner pia-arachnoid membrane - with cerebrospinal fluid filling the space between them. Large cerebral hemispheres extend back to meet a highly developed, deeply convoluted cerebellum, reflecting the delicate balance and precise muscular coordination flight demands; the cerebrum itself controls voluntary movement and serves as the centre for memory and intelligence. The diencephalon, covered by the cerebral hemispheres and cerebellum, relays signals to the cerebral hemispheres, integrates the autonomic system, and processes sensations such as extreme cold, heat and pain; on its ventral side lies the optic chiasma, behind which the infundibulum bears the pituitary (hypophysis). The optic lobes, pushed to a lateral position by the large cerebral hemispheres and cerebellum, are the pigeon's centres for sight, while the small, degenerate olfactory lobes reflect its poor sense of smell. In terms of sense organs, the eyes are large, biconvex rather than spherical, with a bony sclerotic coat and a vascular, pigmented, plaited structure ca …