890 THE NERVES. 



to the two ganglionic enlargements m the region of the neck, either directly, or 

 through the medium of the middle cervical ganglion, when that is present. It is 

 continued backwards with the dorsal portion of the sympathetic chain. 



Afferent Branches. — These are two, proceeding from the cervical pairs. 



One is a thick nerve, satellite to the cervical vertebral artery (sometimes 

 named the vertebral plexus), and lodged with it in the foramina of the cervical 

 vertebrae ; it is formed by filaments emanating from the second, third, fourth, 

 fifth, sixth, and seventh pairs of cervical nerves, and thus carries in a mass, to 

 the sympathetic, the contingent of aiferent nerve-fibres of the majority of these 

 nerves (Fig. 480, 24'). 



The other branch is an isolated one, proceeding from the eighth cervical pair. 



Besides these afferents, there ought to be noticed the filaments sent by the 

 pneumogastric nerve, and which join the middle cervical ganglion, when it is 

 present (see the description of the pneumogastric nerve). 



Efferent Branches. — These are detached from the posterior and inferior 

 parts of the ganglion, and for the most part proceed to the heart. Some extremely 

 fine filaments go to the anterior mediastinum, or pass on to the collateral arteries 

 of the brachial trunk. 



The cardiac nerves (Fig. 480, 5) cross the base of the pericardium, alongside 

 the common aorta, and are then distributed to the tissue of the auricles and 

 ventricles. Some follow the divisions of the pulmonary artery, and concur in the 

 formation of the bronchial plexus. 



To arrive at the heart, these nerves accompany the axillary arteries and the 

 trachea, giving origin, on the inferior face of the latter, to a very large fasciculus, 

 named, in Veterinary anatomy, the tracheal plexus ; this is single, and is traversed 

 from behind to before by the two recurrent nerves, which give or receive from it 

 numerous filaments. 



The cardiac nerves come from the right and left sides. In the Horse they 

 usually have the following disposition : — 



a. On the left side are four nerves, two of which — very fine — proceed from 

 the middle cervical ganglion and disappear on the vessels which arise from the 

 convexity of the brachial arteiy. Of the other two, one is superficial, the second 

 deep. The former — the most voluminous — begins as a filament from the middle 

 cervical ganglion, and passes backwards and downwards, forming an arching 

 anastomosis below the brachial artery with a branch detached from the inferior 

 cervical ganglion, then lies beside the following. The deep nerve is at first 

 formed of three elements : 1. Medullary fibres furnished by the spinal pail's. 

 2. A ramuscule from the cervical cord of the sympathetic. 8. A slender filament 

 which leaves the left pneumogastric, near the entrance to the thorax. It places 

 itself in the direction of the heart, adheres to the superficial nerve, is inflected on 

 the concavity of the brachial artery, margins that vessel on the left, and insinuates 

 itself between the aorta and the pulmonary artery. At this point, these nerves 

 are distributed to the heart and large vessels, a branch passing beneath the 

 right auricle and entering the cardiac muscle ; a second br.mch ramifies on the 

 commencement of the pulmonary artery and on the right ventricle ; two other 

 grey, plexiform branches anastomose more or less between the aorta and pulmonary 

 artery, and unite beneath the arch of the aorta, with a nerve from the right side, 

 then descend in the vertical groove on the heart, to be expended in the left 

 ventricle ; lastly, other ramuscules, parallel to the pneumogastric, go to the 

 pulmonary artery and aorta. 



