24 



7. Cut across the medulla, and then raise the cerebral lobes, and after noting cut 



as near to the skull as possible the following nerves — 



(1) The optic nerves forming the chiasma as they extend towards the 



optic lobes. 



(2) The 3rd, 4th, and 6th nerves which pass to the muscles of the eye. 



(3) The 5th nerve running forwards to escape in front of the auditory 



capsule. 



(4) The 7th nerve passing out of the skull immediately behind the 5th. 

 (.5) The 8th, entering the auditory capsule. 



(6) The 9th and 10th, escaping by an aperture behind the auditory capsule. 



8. Examine and sketch the under surface of the brain (3 nat. size), showing the 



cerebral lobes, the optic chiasma, the tuber cinereum and the pituitary body, 

 the crura cerebri, the medulla oblongata, and the roots of the cranial nerves. 



9. Examine the eye of the frog, and at the same time the eye of the sheep or ox. 



a. The frog — 



(a) Eemove one of the eyes, and note the cornea, and behind it the 

 elliptical pupil surrounded by the iris ; also the sclerotic pierced 

 by the optic nerve. Cut round the equator of the eye and 

 observe (1) the choroid and retina; (2) the vitreous humour 

 filling the cavity of the eyeball ; and (3) in the anterior portion 

 the lens, iris, and aqueous chamber. 



b. The ox or sheep. 



(a) Eemove the muscles and other tissues so as to expose the sclerotic 

 and optic nerve, and note the conjunctiva covering the cornea 

 and extending over the anterior portion of the sclerotic, also the 

 iris perforated by the pupil. 



(&) After puncturing the cornea and noting the aqueous humour which 

 escapes from the anterior chamber, remove the cornea by cutting 

 round the margin, and note the pupil, iris, lens, and posterior 

 chamber, and the ciliary muscle which connects the outer margin 

 of the iris to the cornea and sclerotic. 



(c) Separate the ciliary muscle from the cornea and sclerotic ; remove 

 the sclerotic from the anterior portion of the eyeball ; observe 

 the choroid and the vessels and nerves (ciliary) which reach it 

 through the sclerotic. Raise a portion of the choroid and note 

 the retina, and then after cutting through the choroid and retina 

 by a circular incision midway between the outer margin of the 

 iris and the equator of the eye, remove the lens and the struc- 

 tures in connection with it, and examine under water, noting 

 (1) the anterior portion of the retina (ora serrata) lying within 

 the choroid ; (2) the circle of folds (ciliary processes) in front of 

 the ora serrata projecting from the anterior portion of the choroid 

 to fit into depressions on the outer margin (suspensory ligament) 

 of the capsule of the lens ; (3) the layer of dait pigment (uvea) 

 on the posterior surface of the iris ; (4) the capside of the lens, 

 and the lens after removal from its capsule. 



c. Examine next the posterior portion of the eye, noting (1) the vitreous 

 ' humour enclosed by the delicate hyaloid membrane ; (2) the retina 



lying between the vitreous humour and the choroid with blood vessels 

 radiating in its substance from the point of entrance (blind spot) of 

 the optic nerve; (3) the lustre of the greenish coloured tapetum 

 lucidum. _ 



d. Indicate the structures seen in an ideal section (2 nat. size). 



