x PRACTICAL DIRECTIONS 479 



geal 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 the facial nerve, and immediately 

 below it that of the trigeminal : trace them backwards 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 (ampiillary) 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. 



4. 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 mandibular branches. 



6. T\IQ facial nerve, entering the orbit close behind the maxillo-mandi- 

 bular nerve, and giving off : behind the spiracle a large hyornan- 

 dibular 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. ^^Qglossopharyngealz.^ 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 connective-tissue. 

 Trace the glossopharyngeal to its bifurcation over the first gill- cleft, 

 and in the vagus follow out a, the four branchial branches, forking 

 over the remaining gill-clefts ; b, the visceral branch ; and c, the lateral 

 line branch, above and to the inner side of the branchial branches. 



8. Separate some of the ampullary sensory tubes from one another, 

 and note the ampulla and the nerves supplying them. 



9. Carefully slice away the cartilage of the auditory capsule of the 



