x PRACTICAL DIRECTIONS 479 



cord just behind the medulla oblongata, and through the 

 origins of the cerebral nerves. Remove the brain and place 

 it in formaline or spirit. 



II. Carefully dissect away the skin covering the head and 

 pharyngeal region on the undissected side, expose the orbit, 

 and remove the delicate connective-tissue surrounding its 

 contents. Pin down firmly, and dissect out the following 

 from the side (compare Fig. 125 and pp. 461-464). 



1. The ophthalmic division of t he facial nerve, and imme- 

 diately below it that of the trigeminal ; trace them back- 

 wards to their foramina in the skull-wall and forwards, 

 through a canal between the olfactory capsule and the 

 cranium, to their distribution. 



2. The large mass of sensory (ampullary) canals on the 

 dorsal side of the snout. 



3. The four recti and the two oblique eye-muscles 

 (Fig. 126), and the nerves (III, IV, VI) supplying them. 



i. The eye, and the optic nerve anterior to the recti 

 muscles. The eye may now be removed by cutting through 

 the muscles and optic nerve, and dissected as directed on 

 p. 191. 



5. The large, flat, maxillo-mandibular division of the 

 trigeminal, running forwards and outwards along the floor 

 of the orbit, and there dividing into maxillary and mandi- 

 bular branches. 



6. The facial nerve, entering the orbit close behind the 

 maxillo-mandibular nerve, and giving off : behind the 

 spiracle a large hyomandibular branch, passing along the 

 anterior border of the auditory capsule and posterior wall 

 of the orbit, and down the anterior side of the hyoid arch 

 just beneath the skin : and in front of the spiracle a 

 palatine and prespiracular branches. Of the branches to 

 the sensory canals, the ophthalmic has already been seen ; 

 the buccal and external mandibular require very careful 

 dissection in order to make them out satisfactorily. 



7. The glossopharyngeal and vagus nerves. To expose 

 these, slice away sufficient of the auditory capsule (noting as 

 you do so the semicircular canals and the endolymphatic 

 duct, p. 465) to expose the foramina by which they emerge 

 from the skull, behind the auditory capsule, and separate 

 the mass of muscles lying alongside the vertebral column 

 from the branchial apparatus, by dissecting away the con- 

 nective-tissue. Trace the glossopharyngeal to its bifurca- 

 tion over the first gill-cleft, and in the vagus follow out 

 a, the four branchial branches, forking over the remaining 



