LIVERPOOL VETERINARY MEDICAL ASSOCIATION. 
791 
OPHTHALMIA AND SOME OF ITS CONSEQUENCES. 
The parts generally known by the name of the eye are divided into 
those of vision, viz. the globe or eyeball, and the accessory organs or 
appendages, viz. the eyebrows, eyelids, eyelashes, the muscles of the 
eylids, the tarsal cartilages, the Meibomian glands, the conjunctiva, the 
membrana nictitans, the lachrymal gland, the caruncula lachrymalis, the 
puncta lachrymalia, the lachrymal sac, the ductus ad nasum, and the 
muscles of the eyeball. I think it would be hardly satisfactory to proceed 
•to the consideration of ophthalmia without refreshing our memory with a 
very slight run over the anatomy and physiology of the parts most 
affected. 
The eyeball is contained in the cavity of the orbit, and is composed of 
three tunics: 
1st, Sclerotic and cornea; 
2nd, Choroid, iris, and ciliary processes; 
3rd, Retina; 
And three refracting media, viz. aqueous humour, crystalline lens, and 
vitreous humour. 
The sclerotic is that dense, hard structure, composed of white fibrous 
tissue, forming the posterior five-sixths of the globe; it is not very 
vascular, and the existence of nerves in it is doubtful. It is pierced 
behind by the optic nerve, the arteria centralic retina, and numerous 
small ciliary nerves and vessels. The cornea is the anterior sixth of the 
globe, is fibrous in structure, tough, and unyielding, is perfectly trans¬ 
parent, and consists of five layers, the central, fibrous, or cornea proper, 
the anterior and posterior elastic lamina, immediately before and behind 
the central, the conjunctiva in front, and the lining of the anterior 
chamber behind. 
Neither blood nor lymphatic vessels have been discovered in the cornea, 
the capillaries terminating in loops at its edges. The nerves are very 
numerous, and form a delicate network. 
The second is the vascular and pigmentary tunic of the eye ; it consists 
of the choroid behind, proceeding forwards, and forming the iris ciliary 
processes, and at the junction of the cornea and sclerotic ciliary ligament 
and muscle, it is of a dark brown colour, and consists of three layers, 
external, middle, and internal. 
The external layer consists principally of veins, venae vorticosae, the 
larger branches of the short ciliary arteries proceeding forwards between 
the veins before bending downwards, and star-shaped pigment-cells being 
joined together by a loose delicate network. 
The middle layer, or tunica ruyschiana is formed by the short ciliary 
arteries into an exceedingly delicate plexus of capillary vessels. The 
internal is the pigmentary layer, and consists of a very fine single layer 
of hexagonal nucleated pigment-cells. In albinos these cells contain no 
pigment. 
The iris consists of several layers, and is made up of a delicate inter¬ 
lacement of nerves, vessels, and pigment-cells behind, and muscular fibres 
running in two directions, from within outwards, acting as a dilatator 
and circular as a sphincter. 
The blood is derived from the long and anterior ciliary, and from the 
vessels of the ciliary processes. 
The retina is the internal coat of the eye, and consists in a membranous 
expansion of the peripheral extremity of the optic nerve, for the purpose 
of receiving or absorbing the rays of light from luminous bodies; it pro- 
