IX. The glossopharyngeal nerve divides into four main branches, as follows: (1) to the larynx, (2) to the œsophagus, (3) to the hyomaxillary and sterno-maxillary muscles, and (4) to the tongue. There are also certain communicating twigs with the facial and vagus nerves. X. The vagus or pneumogastric nerve gives off four branches: (1) and (2) communicate with each other and supply the pharynx, larynx, œsophagus, and trachea; (3) goes to the œsophagus; (4) goes to the heart, lungs, and stomach. XI. The spinal accessory nerve. There seems to be some doubt as to the exact identity and distribution of this nerve, but Bronn says that, according to Fischer, it gives twigs to the lower head-muscles and then divides into fine branches in the atlanti-mastoideus muscle. XII. The hypoglossal nerve, going to the region of the tongue, divides into three branches: (1) the median and smallest goes to the sterno-maxillary muscle; (2) the inner and larger goes to the same muscle and also to the coraco-hyoid and sterno-hyoid muscles; (3) the outer and largest divides into three twigs of which the first two lead to the hyomaxillary and sterno-maxillary muscles respectively, while the third divides into two twigs that lead to the hyoglossal and genioglossal muscles respectively. THE SPINAL NERVES As was noted above, the dorsal roots of the first two spinal nerves are lacking. I, II, and III. The ventral branches of these three nerves supply the smaller, ventral neck muscles. IV. The ventral branch of this nerve innervates with its chief divisions the ventral muscles, the sphincter colli, and the integument of the neck, and sends a small branch to the levator scapulæ superficialis muscle. V. The ventral branch of this nerve sends branches to the ventral muscles of the neck, to the levator scapulæ superficialis; a large branch goes to the sterno-mastoid; and the rest of the nerve distributes itself in the sphincter colli and the integument and ventral muscles of the neck. VI. The sixth nerve distributes itself to the ventral musculature and to the integument of the neck, and sends a fairly strong branch to the levator scapulæ superficialis muscle and to the most anterior part of the collo-thoraci-suprascapularis profundus muscle. VII. The seventh nerve is the first to enter, by a small branch, into the brachial plexus (Figure 31). It also sends a branch to the ventral muscles and the integument of the neck, and three branches to various shoulder muscles. VIII. The ventral branch of the eighth nerve (Figure 31) is the second largest nerve of the brachial plexus. It gives some twigs to the ventral muscles and then gives one or two nerves to the collo-thoraci-suprascapularis profundus and the serratus superficialis muscles. The rest of the nerve divides into an inferior and a superior branch which unite with the ninth nerve.