SOS NERVOUS SYSTEM OF THE HORSE 
runs forward on the ventral part of the left face of the trachea, and continues in the 
neck in a position similar to the right nerve. 
_ _ It is worthy of note that the left nerve passes beneath the bronchial lymph glands as it 
winds around the aorta; also that in the next-part of its course it lies between the left surface of 
the trachea and the deep face of the aorta, and is then related to lymph glands which he along 
the ventral aspect of the trachea. The left recurrent is often incorporated in part of its course 
in the anterior mediastinum with a deep cardiac nerve. Further, the left nerve lies at first ven- 
tral to, and then upon, the cesophagus in the neck. The right recurrent is given off from, or in 
common with, a considerable trunk which connects the vagus with the first thoracic ganglion 
of the sympathetic. The arrangement here is commonly more or less plexiform, and from it 
one or two cardiac nerves arise. 
The terminal part of each nerve (Fig. 649) lies on the dorsal surface of the 
trachea, in relation to the cesophagus medially and the carotid artery dorsally.! It 
passes between the crico-arytenoideus dorsalis and the crico-pharyngeus, and 
enters the larynx at the medial side of the lamina of the thyroid cartilage. Before 
entering it gives branches to the crico-arytenoideus dorsalis and arytenoideus 
transversus, and afterward supplies the internal muscles of the larynx. It also 
communicates by delicate filaments with branches of the anterior laryngeal nerve.” 
Collateral branches are given off to the cardiac plexus (Rami cardiaci), to the 
trachea (Rr. tracheales), to the oesophagus (Rr. cesophagei), and to the posterior 
cervical ganglion of the sympathetic. 
4. Cardiac branches (Rr. cardiaci), usually two or three in number, are given 
off from each vagus within the thorax (Figs. 553, 554). These concur with the 
‘ardiac branches of the sympathetic and recurrent nerves to form the zardiae 
plexus, which innervates the heart and great vessels. 
5. Small tracheal and cesophageal branches (Rr. tracheales et cesophagei) 
are given off from both vagi in the thorax. These concur with branches from the 
recurrent nerves and the posterior cervical and anterior thoracic ganglia of the 
sympathetic in forming the posterior tracheal and cesophageal plexuses, from 
which twigs go to the trachea, cesophagus, heart, and large vessels. 
6. Bronchial branches (Rr. bronchiales) are detached at the roots of the lings 
and unite with sympathetic filaments in forming the pulmonary plexuses. From 
the latter numerous branches proceed in a plexiform manner along the bronchi 
and vessels into the substance of the lungs. 
The vagus and glosso-pharyngeal nerves are so closely associated in origin and central 
connections that they may be described together in this respect. 
The sensory fibers arise from the petrous and jugular ganglia, and their central parts enter 
the lateral aspect of the medulla and divide into anterior and posterior branches like the fibers of 
the dorsal roots of the spinal nerves. Most of the fibers end in arborizations about the cells of the 
vago-glosso-pharyngeal nucleus of termination, which consists of two parts. Of these, the dorsal 
sensory nucleus (Nucleus alee cinereze) is situated in the posterior part of the floor of the fourth 
ventricle and in the adjacent part of the closed portion of the medulla near the median plane. 
The other part is termed the nucleus of the solitary tract, and is so named because its cells are 
grouped about the bundle (Tractus solitarius) formed by the posterior divisions of the afferent 
nerve-fibers. It ends about the level of the pyramidal decussation. The secondary central con- 
nections are similar to those of the sensory part of the trigeminus. ; 
The motor fibers (and those of the medullary part of the accessory) arise from the dorsal 
motor nucleus and the ventral motor nucleus. The cells of the former lie in groups along the 
ventro-medial side of the dorsal sensory nucleus. The latter, also termed the nucleus ambiguus, 
is situated more deeply in the lateral part of the formatio reticularis. 
THE SPINAL ACCESSORY NERVE 
The spinal accessory nerve (N. accessorius) is purely motor. It consists of 
two parts which differ in origin and function. 
‘The nerve lies here about a finger’s breadth above the thyroid gland. If, however, the 
gland is enlarged it may come in contact with the nerve. The same is true in regard to the rela- 
tion to the anterior cervical lymph glands. 
2 The recurrent nerves innervate all the intrinsic muscles of the larynx except the crico- 
thyroid. 
