DISSECTION OF THE SHARK 



21 



('81). On the functions of the ears of fishes, see the papers by 

 F. S. Lee and G. H. Parker cited in the Bibliography. For the 

 mammalian ear see Section 80. 



10. Remove the cartilaginous walls of the cranium down to 

 the foramina of the cranial nerves. This can best be done by 

 cutting the cartilage away in thin slices with a sharp knife. The 

 foramen of the slender IV nerve will be first exposed, lying me- 

 dially of the eyeball and far dorsally. The other foramina lie 

 farther ventrally. 



11. Note the membranes (meninges) of the brain. The 

 dogfish brain is closely enveloped by a single membrane. Be- 

 tween this and the perichondrium which lines the cartilaginous 



/,„ i^-yj ' ■ 



s. Supra-orbital trunk r 



Optic lobe ^ 



**~^Mjt*-ajL*-~ , Epithalamus^ 

 Thalamus 



/Acoustico-lateral area 

 -Gang, lateralis VII 



/Gen. cutaneous area 

 r. lateralis X 



.vaJWv^S 



t*X*t 



*ol£. 



igrfifeph? 



Somatic area n. W.y/ 

 Hypothalamus yS 



c ^ , Z^r/ | \ > «L n.li n.A 



s j(^r / ^\— t^" 1 "- hyomandibularis VII 

 ^s^ / ^^— Spiracle 



Ganglion V^ ^ 

 Infra-orbital trunk ^ 



/ ^r. palatinus VII 

 Ganglion geniculi VII 



xxV- 



Fig. 3. — The same brain as Fig. 2 seen from the side and slightly enlarged. 

 (From Herri ck's Introduction to Neurology.) 



cranium is a very loose arachnoidal tissue which is not, however, 

 condensed into a definite arachnoid membrane, as in mammals 

 (cf. Section 45). 



VI. Carefully dissect out the cranial nerves and eye-muscles of 

 the right side. The/ optic nerve, eye-muscles, and eye-muscle 

 nerves (III, IV, and VI pairs) are arranged practically as in 

 the human body. Consult your anatomies for names and de- 

 scriptions and determine the action of each of the eye-muscles. 

 Notice the long ciliary nerves distributed to the eyeball and 

 trace their connections, if possible, with branches of the third 

 and fifth nerves. 



