THE THYROID NERVE IN THE DOG AND ITS FUNCTION

¹ The Department of Physiology, Faculty of Medicine, University of Manitoba

The thyroid nerve described by Nonidez in puppies and canine ftuses has been found in adult dogs.

It is usually made up of nerve fibres derived from the superior cervical ganglion of the sympathetic and from the superior laryngeal branch of the vagus. The vagus fibres may arise from the ganglion nodosum or the vago-sympathetic trunk, and occasionally from the external laryngeal nerve.

The thyroid nerve terminates in branches which enter the thyroid with the branches of the superior thyroid artery.

Stimulation of the thyroid nerve consistently slows the flow of blood through the gland. Acceleration of the blood-flow has been obtained by stimulating the ipsilateral vagus and, in one instance, fibres from the external laryngeal nerve.

These results, indicating that the thyroid has a constant constrictor and some dilator innervation, suggest an indirect nervous control of the output of thyroid hormone into the blood-stream.

Histological changes in the thyroid, after electrical stimulation of the thyroid nerve for some hours, could not be demonstrated. Section of the nerve, allowing time for degeneration, produced no demonstrable histological change.