IX PRACTICAL DIRECTIONS 463 



3. The four recti and the two oblique eye-muscles (Fig. 117), 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, noting its structure as 

 before. 



5. The large, flat, niaxillo-niandibular division of the trigeminal, 

 running forwards and outwards along the floor of the orbit, and there 

 dividing into maxillary and mandibular branches. 



6. The facial nerve, entering the orbit close behind the maxillo-mandi- 

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

 dilular 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 prespiracnlar 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 glossophary ngeal &xvA vagus nerves. To expose these, slice away 

 sufficient of the auditory capsule (noting as you do so the semicircular 

 canals and the endolymphatic duct) 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 glosso- 

 pharyngeal 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 ampuUary sensory tubes irom one another, 

 and note the ampulla and the nerves supplying them. 



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

 side you have not already dissected so as to expose the membranous 

 labyrinth. Examine under water, and make out the vestibule with its 

 contained otolithic mass, the three seviicircular canals with their 

 ampullce, and the branches of the auditory nei've (compare Fig. 59). 



III. Now examine the preserved brain from above, from below, and 

 from the side, making out, in addition to the parts already noticed 



(§ F, I, I)- 



I. The optic chiasma, inhindibulum — with an oval swelling and a 



