IV. OF RANA PIPIENS. 43 



of the neck, crosses the vagus and its laryngeal branch, and, running nearly paral- 

 lel to the glosso-pharyngeal, passes along the genio-hyoid muscle as far as the 

 symphysis of the lower jaw ; it then ascends, in company with the last-mentioned 

 nerve, into the substance of the tongue, and is lost among its muscular fibres. This 

 description applies to the principal trunk ; in its progress, however, it gives off nu- 

 merous branches, repeating very nearly the distribution of the same nerve in the 

 human body ; in other words, it is distributed to the muscles which move the os 

 hyoides and tongue. The following branches were traced : 1st, a branch to the 

 muscles attached to the vertebral column in its immediate neighborhood and to the 

 omo-hyoid ; 2d, to the sterno-hyoid ; 3d, to the hypoglossus ; 4th, genio-hyoid ; 

 5th, genio-glossus. Galvanism proves still further the relation of these muscles to 

 the hypoglossal nerve ; if this agent be applied to the main trunk near the verte- 

 bral column, convulsions are simultaneously produced throughout the whole hyoid 

 and glossal group ; but nothing of the kind is noticed, as has already been stated, 

 when it is applied to the glosso-pharyngeal, which has a direction so nearly parallel 

 with it.* On entering the base of the tongue, the hypoglossus, like the glosso- 

 pharyngeal, is thrown into zigzag folds, which adapt it to the peculiar extensibility 

 of that organ. 



The descriptions of this nerve by different anatomists are somewhat discordant, 

 and it is therefore a matter of some interest that they should be compared. Vogt, 

 in the memoir already referred to, says : " Volkman describes this nerve as the first 

 nerve of the neck, which it is according to its exit, but not according to its origin 

 and its course. He also represents its origin as at some distance from the vagus, and 

 the nerve as if it were provided with a ganglion. I thought I could at least find the 

 last in Frogs, but was soon convinced of my error." " The hypoglossus takes its origin 

 close to the vagus, but nearer to the median line, from the under surface of the 

 medulla oblongata, and, instead of going directly outwards, bends backwards close 

 to the under side of the medulla within the pia mater, and when opposite to the 

 foramen makes a sudden bend outwards, so that, if the pia mater is untouched, it 

 has the appearance of having its origin opposite to the hole, and at some distance 

 from the vagus. Has Volkman been deceived by this disposition 1 " " That, as 

 Volkman says it does in Frogs, it takes its origin with two roots, and has, as he 

 draws it, a ganglion, is certainly not the case in Toads, and I believe that no error 

 on my part exists." Stannius distinctly, but incorrectly, asserts, that the hypo- 

 glossus has no posterior roots. " The spinal nerves always arise by two roots ; the 

 first two cervical nerves appear to form an exception to this rule, not only in the 

 naked Reptiles, where they take the place of the hypoglossus, but also in some of 

 the scaly ones." f 



According to the dissections which form the basis of this memoir, Volkman's 

 description is quite correct, both as to the existence of two kinds of roots and of 

 the ganglion ; also as to the position on the side of the medulla. The roots of the 



* The same result, as regards its function, is shown by the experiments of Dr. Waller. Philosophical 

 Transactions, 1850. 



t Stannius, Manuel d'Anatomie Comparee, Tom. II. p. 200. 



