Practical anatomy: a manual of dissections / by Christopher Heath.

  • Christopher Heath
Date:
1870
Catalogue details

Licence: Public Domain Mark

Credit: Practical anatomy: a manual of dissections / by Christopher Heath. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

    552/600 (page 542)
    The lens is bi-convex, but the posterior surface has a greater curve than the anterior. It is perfectly transparent in health, but has a complicated structure consisting of fibres arranged around three axes running in difierent directions, of which indications are usually visible in the bullock's eye [and which can be seen by boiling the lens or hardening it a while in alcohol]. The exterior of the lens readily breaks down, but the interior or nucleus is very dense. The Canal of Petit (Fig- 246, cp) is [the circular canal between the two layers into which the hyaloid membrane divides anteriorly. On section it is of course irregularly triangular]. [Take a Fourth Eye and remove the sclerotic and cornea as described on p. 537. Then, carefully lifting the choroid by one pair of forceps, it can be torn by a second. Once that the tearing is begun, it is easy to continue till the choroid is removed, from the nerve up to the ciliary muscle. Some of the internal (pigmentary) layers of the cho- roid will adhere in spots to the retina, and may be readily examined by the microscope. Float some of the outer layers of the choroid in the water, and the tortuous vence vorticosce will be readily seen. Lift up the ciliary muscle carefully and divide it antero-posteriorly. Its thickness can thus be appreciated. By seizing one edge of the cut and lifting it, the entire retina and vitreous will separate from it by its weight, but it may need a little scraping with the knife handle. The ora serrata and the zone of Zinn are thus admirably shown.] The Retina (Figs. 243, 9, p. 534) is the nervous coat of the eye and its essential part. It lines the choroid coat, being connected posteriorly with the optic nerve, and extends in front nearly as far forward as the ciliary body, where it terminates about one-eighth of an inch behind the margin of the cornea in a finely jagged border, the ora serrata. During life the retina is trans- parent, so that the vascular choroid can be seen through it with the ophthalmoscope, but after death it has a grayish color and is thrown into folds, owing to the diminution of the tension of the globe. The entrance of the optic nerve may be seen about one- tenth of an inch [20°] to the inner side of the axis of the eye, and radiating from this may be seen the branches of the arteria centralis 7-etinee, which enters the eye at this point, and its accompanying veins. In the axis of the eyeball in the human eye [but not in that of quadrupeds]