22 GUIDES FOR VERTEBRATE DISSECTION 



Draw a dorsal view of the brain from above, X 4, leaving space 

 on one side of the sheet for the cranial nerves to be made out later. 

 Name the parts on the drawing. 



The Eye. Dissect out the loose connective tissue above and 

 internal to the eye, taking great pains not to injure muscles or 

 nerves. Two muscles will be found attached to the upper medial 

 surface of the eye, in front the superior oblique, farther back the 

 superior rectus. Pull the eye outwards and note the point of 

 attachment (origin) of these muscles on the side wall of the skull. 

 See the fine nerve (trochlearis, IV) running from the wall of the 

 skull to the superior oblique muscle. (Its intracranial course 

 was noted earlier.) Dorsal to this and just lateral to the wall of 

 the skull is a longitudinal nerve, the ophthalmicus superficialis. 

 the origin and distribution of which will be traced later. 



Pull the eyeball outwards and notice the external rectus 

 muscle attached to its posterior surface, and the internal rectus 

 inserted on the ball just below the superior oblique. Their 

 origins are near that of the superior rectus. Compare with your 

 own eye and see why these terms external and internal are used. 



Cut these muscles close to the eyeball and roll the eye out- 

 wards so as to see two other muscles, the inferior rectus attached 

 to the lower surface of the ball, the inferior oblique to its anterior 

 surface beneath the internal rectus. Also note the attachment 

 of each muscle to the cranium. 



Two other connections may be noted now, the optic nerve, II, 

 which proceeds from the cranium to the medial side of the eye; 

 and the optic pedicel, a cartilaginous rod with expanded distal 

 end which abuts against the eyeball. Crossing the inner surface of 

 the ball below the superior rectus is the ophthalmicus profundus 

 nerve. See its entrance into the orbit below the main trunk of 

 the ophthalmicus superficialis and its exit in front. Jil, 



Cut all the muscles and nerves loose from the. eye close to 

 the ball and then dissect away the lid and remove the eyeball. 

 Make a sketch of the ball and its muscles viewed from the medial 

 side. 



Is the eyeball spherical or is any part of it flattened? Lay 

 it open by a cut around the equator and study the two halves in 

 water. 



In the inner half make out an outer cartilaginous layer, the 

 sclera, against which lies a darkly pigmented choroid coat, 



