ANATOMY OF THE FROG 67 



the inner end of this, it turns down to the eustachian tube and 

 angle of the mouth. The seventh is joined close to the 

 columella by a branch from the ninth. 



The eighth, or auditory nerve, arises from the medulla, 

 immediately behind the seventh, goes straight through a 

 foramen in the auditory capsule to the ear, and supplies the 

 organ of hearing. 



The ninth, or glossopharyngeal nerve, arises, in common 

 with the tenth nerve, from a number of roots on the side of the 

 medulla, behind the auditory nerve. It passes, in company 

 with the tenth nerve, through a foramen at the back of the 

 cranium just in front of the occipital condyle, and divides into 

 two branches, an anterior, which runs forward to join the facial 

 nerve close to the columella, and a posterior, which curves 

 downward and inward to the floor of the pharynx, along 

 which it runs, supplying the petrohyoid muscles and the 

 mucous membrane of the tongue and pharynx. 



The tenth, pneumogastric or vagus nerve, is a very 

 important nerve with complicated relations. After leaving the 

 skull in company with the ninth nerve, it enlarges to form a 

 ganglion, the ganglion nervi vagi. The nerve runs backward 

 and ventralward along the side wall of the pharynx, and 

 finally divides into several branches, of which the most 

 important are : (i) the nervus recurrens or laryngeus, which 

 arrives at the posterior cornu of the hyoid, and turns forward to 

 pass beneath it and the pulmo-cutaneous artery, whence it runs 

 forward close to the middle line, to end in the larynx ; (2) 

 the ramus cardiacus, which runs along the dorsal surface of 

 the pulmonary artery and the superior vena cava towards the 

 sinus venosus, where it joins its fellow of the opposite side, and 

 the two pass on to the auricular septum of the heart ; (3) the 

 rami gastrici, which run through thepartial diaphragm formed by 

 the insertion of the internal oblique muscle upon the walls of the 

 oesophagus, and are distributed to the walls of the stomach ; (4) 

 the rami pulmonales, which also perforate the partial diaphragm, 

 and then follow the course of the pulmonary artery to the lung. 



The sympathetic nervous system (see fig. 10) is intimately 

 connected with both spinal and cranial nerves. It is a chain of 

 paired nervous ganglia, joined together by longitudinal cords, 

 lying on either side of the vertebral column, and each ganglion 

 makes connection with a spinal nerve by a short branch, the 



