Fiber size and sensory endings of the middle cardiac nerve of the domestic fowl (Gallus domesticus).

The middle cardiac nerve, a branch of the vagus, innervates the ventricles of the avian heart. Of 533 myelinated sensory fibers, the size range was 2 micron. The ratio of myelinated to unmyelinated sensory fibers ranged from 2.17 to 3.48. Sensory endings resembled a network pattern with no distinct receptor-like endings. Frequency of nerve population increased from apex to base of the heart.