VAN 121: Veterinary Gross Anatomy-II (2+2)

VASCULAR AND NERVOUS TUNIC

Dissection 

• Now a horizontal meridional section of the eyeball at the level of the dorsal one third of the cornea is required.
• To make this first incise the cornea at its dorsal one third with a sharp razor blade and allow the aqueous humour to spurt out.
• Insert pointed end of the sharp pointed scissors in a horizontal plane. While cutting be careful not to injure the lens.
• Study in the smaller segment, the details of the chorioid and ciliary body after peeling the vascular coat from the sclera.
• The chorioid is a dark brown vascular membrane but above the optic papilla is an area having metallic lustre, the colour varying from iridiscent blue to green, the tapetum. 

• The ciliary body consits of the ciliary rings, the ciliary proceeses and ciliary muscle. The ciliary proceeses from a circle of radial folds and give attachment to the zonula ciliaris on the suspensory ligament of the lens. (Examine this in the section with the lens intact). This ciliary muscle is on the outer part of the ciliary body and appears as a white circular band.
• Study the iris and note the concentric and radial folds on its anterior face. Corpora nigra may be seen in some specimens along the upper pupillary border.
• Study the boundaries of the anterior and posterior chambers, the refractive media and suspensory ligament of lens in the section with the lens intact.
• Remove the vitreous body and lens, carefully retaining the retina.
• The lens is a biconvex transparent body, the posterior surface of which is more covex and rests in the fossa hyaloidea of the vitrous body. The lens substance consists of transparent lens fibres and is enclosed in a capsule. The capsule at the equator of the lens gives attachment to the suspensory ligaments of the lens. Click here to know more...
• The Vitreous body is a transparent jelly like substance situated between the lens and the retina.
• The retina forms the innermost tunic of the eyeball and appears as a thin membrane, which becomes opaque after death and it, consits of three parts, the Pars optica, the Pars ciliaris and the Pars iridica. The pars optica is limited by a circular line the ora ciliaris retinae at the region of the ciliary body.
• The optic papilla is the point of exists of the optic nerve.