THE CRANIAL OR ENCEPHALIC NERVES. 849 



ganglion. The ganglion itself furnishes the superior laryngeal nerve, which gives off, as in 

 Man, the external laryngeal nerve. 



There is nothing to indicate in the pharyngeal nerve, its disposition being absolutely the 

 same as in the Ox. 



In the Dog, the superior laryngeal nerve has a curious disposition, whicli has not yet, to 

 our knowledge, been described. Reaching the inner face of the thyroid cartilage, it gives off, 

 as in the other animals, filaments to the glottis, epiglottis, liase of the tongue, and oesophagus; 

 but the ramuscule of Galien, which nearly equals the superior laryngeal in volume, does not 

 anastomose with the inferior laryngeal ; it gives a large branch to the crico-arytaeiioid muscle 

 in passing to its surface, and then leaves the larynx to the inside of the recunent, descending 

 on the trachea as far as the entrance to the chest. In that cavity, the descending branch of 

 the superior laryngeal forms two divisions that communicate with the ramuscules of various 

 other nerves passing into this region. On the right side, the largest division receives a 

 voluminous branch from the inferior cervical ganglion; then the two divisions unite, and join 

 the pneumogastric after it has turned round the brachial trunk, a little behind the point of 

 emergence of the inferior laryngeal. 



On the left side the same arrangement is found; the anastomoses are larger and more 

 numerous than on the right siie; the branch follows, in an inverse direction, the course 

 pursued by the recurrent nerve, to join the pneumogastric at the part where the recurrent 

 originates from the latter. 



In this course, the branch gives large ramuscules to the oesophagus and trachea ; those 

 distributed to the former either pass along the muscular tunic and return again to the nerve, 

 or continue along the surface of that tube. In all cases, there is found on the sides of the 

 oesophagus a rich plexus formed by these filaments, as well as by those coming from the 

 pharyngeal nerve. 



• This branch also offers other peculiarities. Thus, it is very often found alongside tlie 

 laryngeal nerve for some distance, and sometimes at several points. When this happens in 

 the upper part, at tiie larynx, as occurs in many cases, it appears to have an anastomosis as 

 in the Ox ; but it is always easy to separate the two nerves, even in fresh specimens, and this 

 separation is greatly facilitated if the piece lias been steeped in water acidulated by nitric acid. 



In the cervical portion, the pneumogastric nerve is closely united to the sympathetic, the 

 separation of the nerves being no longer possible as in the Horse and Ox. 



We have already described a portion of the inferior laryngeal nerve, in speaking of the 

 tracheo-oesophageal branch of the superior laryngeal. Comparison with otiier animals requires 

 that we should transfer the latter to the recurrent. In the Dog, the inferior laryngeal rises by 

 two distinct branches, a short distance from each other, on the right and left aides; these may, 

 or may not, lie together for some distance, but they never become fused. The external part of 

 the nerve receives at intervals filaments proceeding from the superior laryngeal branch, and it 

 rarely gives very fine twigs to tiie trachea and oesophagus. The conimunicatious with the 

 cardiac and tracheal nerves are also chiefly made by the tracheo-oesophageal branch. 



The bronchial nerves are large and numerous. 



The oesophageal plexus, which is furnished by the nerves of the same name, is larger and 

 finer than in the Horse. 



There is nothing to note particularly in the termination of the nerves in the stomach. 



The hypoglossal gives a long branch that passes to the sides of the larynx, and enters the 

 muscles on the anterior face of tlie trachea. 



Rabbit. — We shall only notice some differences in the facial and pneumogastric nerves. 



The facial gives two or three fine branches to the temporo-auricular nerve, on its sub- 

 parotideal course. When these two nerves reach the anterior border of the parotid, they are 

 parallel to and superposed on each other, and it is only on the middle of tht; masseter that the 

 temporn-facial plexus is formed. Sometimes the branch for the risorius of Santorini is detached 

 before the formation of the plexus. 



The pneumogastric has a gangliform plexus, like that of Carnivora. In the cervical region, 

 it is isolated from the filament of the sympathetic. The Rabbit has a sensitive heart-nerve, 

 discovered by Ludwig and Cyon, and named by them the depressor nerve of the circulation. It 

 usually begins by two roots — one furnished by the pneumogastric, the other by the superior 

 laryngeal nerve. It descends along the neck, beside the cord of the sympatlietic, receives — on 

 entering the thorax — ramuscules from the first thoracic ganglion, and is soon lost in the substance 

 of the heart. The root from the superior laryngeal should be the largest, as Toussaint has 

 always found it, while he has rarely seen that which is detached before the formation of the 

 plexus. 



