I04 ELEMENTARY BIOLOGY. [CHAP. 



There will be found to arise immediately 

 external to its ganglion a small dorsal f-amus ; 

 note that this is distributed to the muscles 

 and other parts of the body dorsally, much as 

 is the main trunk or vejitml ramus ventrally. 



4. The cra7iial nen^es. 



The study of these may be greatly facilitated by 

 placing the animal when dead in \ per cent, chromic 

 acid solution, the same to be frequently changed 

 until decalcification is complete. This done ; wash 

 well under running water and preserve in methylated 

 spirit, slightly dilute. 



i. Dissect from the ventral aspect as directed at § 3, 

 leaving the floor of the mouth intact. 



a. The 9/// or glossopharyngeal nerve. Its trunk ; 

 seen, on removing the middle portion of the 

 mylohyoid muscle (Sect. B. c. y) lying immedi- 

 ately external to that of the hypoglossal nerve 

 (§ 3- ^- ") ') ^^^ branches^ seen, on dissecting the 

 genio-hyoid, to be distributed to the tongue and 

 some of its muscles. 



ii. Remove the floor of the mouth together with the 

 heart and gullet, leaving the mandible and a small 

 portion of the mylohyoid muscle on one side. 

 Raise the mucous membrane of the roof of the 

 mouth with forceps and dissect it away with the 

 utmost care, being especially cautious to avoid re- 

 moving certain nerves which lie in close aj^po- 

 sition with it. Next slice away the floor of the 

 cranium and auditory capsules so as to expose 

 their internal cavities; wash clean and examine 

 in water under a hand lens. 



