74 A MANUAL OF ZOOLOGY 



breaking through the floor of the bone cavity of the middle 

 ear. The inner end of the columella expands into a small 

 disk, which fills the foramen ovale, which lea.ds into the 

 vestibule of the inner ear. Enlarge this opening very care- 

 fully and you will find the semicircular canals. Dissect 

 out the eye, noting' the following points: the nictitating 

 membrane, the lachrymal gland ventral to Wie posterior 

 angle of the eye in the orbit (what is its position in man?), 

 the colored Iris, the transparent cornea, which is surround- 

 ed by a peculiar cartilage-like differentiation of the scler- 

 otica. Open the cornea carefully and observe the aqueous 

 humor and how the iris is spread out. Take out the lens. 

 How does It compare with that In the fish and in the frog? 

 Back of the lens find: the vitreous humor, the retina, the 

 choroid coat, and the entrance of the optic nerve. What 

 separates the two eye orbits? Open the olfactory cavities. 

 .Are they lined with any sort of epithelium? How do tljey 

 compare with that in the dog-fish and in the teleost? 



Dissect out the brain very carefully, beginning with 

 the already exposed ends of the olfactory nerves. "Note 

 onr the dorsal aspect the olfactory lobes, the comparatively 

 large cerebral hemispheres, the pineal gland, or epiphysis, 

 the corpora bigemina (optic lobes), the cerebellum, the 

 medulla oblongata, and the fourth ventricle. On its ven- 

 tral aspect note the olfactory lobes, the optic chiasma, the 

 optic nerves, the optic tracts, the pituitary body, the in- 

 fudlbulum, the thalamencephalon, the crura cerebri, and 

 the anterior pyramids of the medulla- oblongata. Make 

 drawings of the dorsal and of the ventral parts of the 

 brain to shoW' the preceding points. 



Dissect out a portion of the. spinal cord. How does 

 it compare with the other forms? How many neck verte- ' 

 brae are there? Dissect out and clean all of the neck 

 vertebrae noting particularly the manner of their articula- 

 tions. Make a note of the different ways they articulate. 

 Dissect out some of the caudal vertebrae and -note their 

 manner of articulation. Dissect out the pectoral girdle. Note 

 the glenoid fossa at its outer extremity for articulation with* 

 the head of the humerus. Articulating with this latter are 

 the radius and the ulna. Are they separate bones? How 



