[Illustration: Fig. 43--Showing method of cutting through the cornea and completing the two sagittal sections.] The two specimens may be kept indefinitely by placing them in a 3 per cent. formaldehyde solution. It will be well to remove the lens from one of the specimens, because it will give better opportunity to see the anatomical relationships. Also, these specimens should be mounted, one above the other, between two pieces of glass, before placing them in the receptacle that is to hold them. Much can be studied in such specimens. Moreover, they present to view the various parts of the organ of vision in such an impressive way, that one does not soon forget the wonderful appearance of the construction of this, Nature’s perfect camera. (Fig. 44.) [Illustration: Fig. 44--Sagittal section enlarged.] If another eye is cut into two parts, additional interesting specimens may be procured; for instance, one showing the presence of the second coat only, the retina having been torn out. Another good specimen may be made by removing all of the inner tissues, and leaving only the sclerotic and cornea. This specimen will show that the first coat is almost entirely a coat which affords strength and protection to the parts that lie within. THE PAPILLA, PUNCTA LACRIMALIA, AND NASAL DUCT The only way to dissect the lacrimal apparatus, other ocular accessories, and the extrinsic muscles, is to procure the head of some animal, preferably a calf’s head, because of its size. Any butcher will supply one for from forty to sixty cents. Have the lower jaw removed. It will make a less bulky piece of material to handle. Close to the inner canthus, on the inner side of each lid, will be found a little rounded eminence--lacrimal papilla--in the centre of which is a small opening--punctum lacrimalis. Both may be seen better on the lower lid, if it is pulled down, and on the upper lid, if it is pulled up. [Illustration: Fig. 45--Showing only a part of a calf’s head and the knitting-needles inserted in the puncta. (Page 94.)] [Illustration: Fig. 46.]