Chap. XL] THE BRAIN AND NERVES. 223 



sequently gives rise to (a) a pulmonary branch, passing to the 

 lung, (b) a cardiac branch passing to the septum, between the 

 auricles of the heart, and (c) gastric branches to the walls of the 

 stomach. 



The following points should be made out by practical dissec- 

 tion : 



1. Place the frog upon its side and remove the integument 

 from the side of the head. On dissecting away the muscles 

 just behind the tympanum, and carefully removing the anterior 

 part of the supra-scapula, four nerve-threads will be seen, three 

 taking their origin from the skull, the fourth from the spinal 

 column. This last is the hypo-glossal (1st spinal nerve). 

 Traced downwards it is found to be distributed to the 

 muscles of .the tongue. From the ventral aspect it is readily 

 seen running beneath the thin transverse sheet of muscle (mylo- 

 hyoid), between the two rami of the lower jaw. Near it, but 

 somewhat deeper, and also distributed to the muscles of the 

 tongue, is the glosso-pharyngeal (ninth cranial). This is continu- 

 ous with one of the three cranial nerves seen just behind the 

 tympanum. The other two are the laryngeal and splanchnic 

 branches of the vagus. 



2. Dissect away the integument and muscles from the rami 

 of the lower jaw. The mandibular branches of the V. lie 

 on their outer faces ; the mandibular branches of the VII. on 

 the inner. Traced backwards, one of these, the mandibular, is 

 found to run up beneath the squamosal bone to the skull. It is 

 a branch of the trigeminal. The other may be traced to the 

 angle of the lower jaw, and thence upwards over the columella 

 and forwards into the skull. It is a branch of the facial. 



3. Detaching or holding widely open the lower jaw, remove 

 the mucous membrane of the palate. Two nerves (one on each 

 side) are seen running from just in front of the guard of the 

 para-sphenoid, where they emerge from the skull, to the vomers. 

 They are the palatine divisions of the facial. By carefully 

 dissecting the guard away on one side the Gasserian ganglion 

 may be exposed. 



4. Just on the lower edge of the orbit, beneath the eye 



