distributed to the tongue, and are the motor nerves of that organ. THE GREAT SYMPATHETIC. A double chain of nervous ganglia extends from the superior to the inferior parts of the body, at the sides and in front of the spinal column, and is termed, collectively, the system of the _great sympathetic_. These ganglia are intimately connected by nervous filaments, and communicate with the cerebro-spinal system by means of the motor and sensory filaments which penetrate the sympathetic. The nerves of this system are distributed to those organs over which conscious volition has no direct control. [Illustration: Fig. 61. Course and distribution of the great Sympathetic Nerve] Four of the sympathetic centers, situated in the front and lower portions of the head, are designated as the _ophthalmic, spheno-palatine, submaxillary_ and _otic ganglia_. The first of these, as its name indicates, is distributed to the eye, penetrates the _sclerotic membrane_ (the white, opaque portion of the eyeball, with its transparent covering), and influences the contraction and dilation of the iris. The second division is situated in the angle formed by the sphenoid and maxillary bone, or just below the ear. It sends motor and sensory filaments to the palate, and _velum palati_. Its filaments penetrate the carotid plexus, are joined by others from the motor roots of the facial nerve and the sensory fibres of the superior maxillary. The third division is located on the submaxillary gland. Its filaments are distributed to the sides of the tongue, the sublingual, and submaxillary glands. The otic ganglion is placed below the base of the skull, and also connects with the _carotid plexus_. Its filaments of distribution supply the internal muscles of the _malleus_, the largest bones of the _tympanum_, the membranous linings of the tympanum and the _eustachian tube._ Three ganglia, usually designated as the _superior, middle_, and _inferior_, connect with the cervical and spinal nerves. Their interlacing filaments are distributed to the muscular walls of the larynx, pharynx, trachea, and esophagus, and also penetrate the _thyroid gland_. The use of this gland is not accurately known. It is composed of a soft, brown tissue, and consists of lobules contained in lobes of larger size. It forms a spongy covering for the greater portion of the larynx, and the first section of the trachea. That it is an important organ, is evident from the fact that it receives four large arteries, and filaments from two pairs of nerves. The sympathetic ganglia of the chest correspond in number with the terminations of the ribs, over which they are situated. Each ganglion receives two filaments from the intercostal nerve, situated above it, thus forming a double connection. The thoracic ganglia supply with motor fibres that portion of the aorta which is above the diaphragm, the esophagus, and the lungs.