glands lie in the lids near the conjunctival surface, and they open behind the cilia at its edge. They are long, shrub-like follicles, analogous to the sebaceous glands, and they pour out an oily matter which prevents the adhesion of the lids or the overflow of tears. There are about 30 in the upper lid. The caruncle is a small mass of sebaceous glands which lies in the inner canthus, and pours out a white secretion; outside it is the plica semilunaris a little fold rudimentary of the nictitating membrane, so highly developed in birds and some mammals. The lacrymal gland lies in the upper and outer angle of the orbit; it is about the size of a small bean, and in structure similar to the salivary glands, but has 6 or 8 ducts. The tears contain water and a little chloride of sodium, and mucus. After washing across the cornea, they pass into 2 small apertures-the puncta, which are kept open and apart by Horner's muscle, the tensor tarsi, which is composed of striped and very red fibres, and is supplied by the facial nerve. The tears flow through the puncta into the lacrymal sac, and then through the nasal duct, which, after running downwards and outwards for an inch and a-half, opens by a valvelike slit into the inferior nasal meatus.

The orbits are conical bony recesses, so arranged that great range of vision is allowed; thus, the eye can play 90° outwards, 60° inwards-comprising a horizontal range of 150°. Upwards it can be thrown 50, downwards 70°-a vertical range of 120°. In these cavities there are 7 muscles, 6 of which are attached to

and

the globe of the eye. The 4 recti are fixed behind at

the optic foramen, and are inserted in the sclerotic, about 4 lines behind the cornea. They can thus turn the eye in 4 directions, and can retract it within the orbital socket. The oblique muscles are 2-a superior, which runs through a beautiful pulley, which is for the purpose of reflecting its tendon towards the outer and back part of the eye, so that it can turn the cornea down

wards and outwards; and the inferior, which is different from the other orbital muscles in arising from the anterior part of the floor of the orbit, and which turns the cornea upwards and inwards. Both oblique muscles can converge and advance the eyes, and can roll them on their antero-posterior axis. The orbital muscles and

Deeper Dissection.

1. Globe. 2. External rectus. 3. Section of Superior rectus. 4-6. Superior oblique. 5. Its pulley.

a. Internal carotid giving off ophthalmic. 2. Elevator of the upper lid. 3. Lacrymal gland. 4. Superior oblique. 5. External rectus. 6. Optic nerve. vessels are here represented. The motions of the eyeball are greatly facilitated by an admirable smooth capsule discovered by Dr. O'Ferrall of St. Vincent's Hospital. He exposed it by dividing vertically the lids and reflecting the segments; and by following these directions I

have always succeeded in demonstrating it to the class at the Royal College of Surgeons. In an exhaustive

paper in the "Dublin Journal of Medical Science," July, 1841, its discoverer thus sums up its physiological and pathological relations: "The reflections suggested by a review of the cases which led to the present inquiry, as well as of this new and curious mechanism itself, may be reduced to the following propositions :

"1st. That the description of anatomists, which places the globe of the eye in contact with the fat and muscles of the orbit, is erroneous.

"2nd. That there exists a fibrous tunic, investing and insulating the eyeball, and separating it from all the other structures in the orbit.

3rd. That the uses of this tunica vaginalis oculi are to present a smooth surface, facilitating the movements of the eye, and, by its density and tension, to protect it from the pressure incidental to the swelling of the muscles during their action.

"4th. That the openings in this tunic perform the offices of pulleys-giving a proper direction to the force exerted by the muscles, securing the motions of rotation, and of opposing those of retraction, which would otherwise predominate.

"5th. That certain cases of disease within the orbit, accompanied by protrusion of the eye-ball, are to be explained only by reference to the tunica vaginalis oculi, and the other fibrous tissues now described.

"6th. That a correct knowledge of the anatomy of the orbit, and of the fibrous structures alluded to, is essential to the operating surgeon in dealing with abscesses and tumours, in extirpation of the eyeball, in the operation for strabismus, and all operations on that cavity."

I will return to the pathological aspects of this structure in the second section of this work.

In the cuttle-fish a serous sac lies between the eye and

its orbit; this has been described as the analogue of the conjunctiva by Cuvier, and of the membrane of the aqueous humour by Owen; but it seems to me closely to resemble the tunica vaginalis oculi.

The cranial nerves accessory to vision are the oculomotor, trochleator, ophthalmic division of trifacial, abducens, and facial, and the sympathetic also contributes some filaments.

The Oculo-Motor, or 3rd nerve, arises in the locus niger of the crus cerebri, and just behind the orbital foramen, splits into an upper and lower branch, which are respectively distributed to the levator palpebræ and superior rectus, and to the inferior oblique, internal and inferior rectus. By sending the motor twig to the lenticular ganglion, it supplies the circular muscular fibres of the iris and the ciliary muscle. The nerve is purely motor, as shown by its distribution, and by its size being proportioned to the development of the muscles in various animals; thus, in the falcon, which has powerful iridal and ciliary muscles, the nerve is as large as in man. Its function is also demonstrated by galvanic stimulation and section. It presides over contraction of the pupilbeing thus antagonistic to the sympathetic-over adjustment, and produces convergence of the eyes, which always concurs in near vision. As the eye is turned upwards and inwards, and the pupil contracted during sleep, it is supposed to be then still in action. Disease of the nerve is indicated by ptosis, divergent strabismus, mydriasis, or dilated pupil, and—as I lately ascertained in a patient of mine in St. Vincent's Hospital-by impaired ocular adjustment. Belladonna produces precisely similar effects. The calabar bean, either by stimulating the third nerve or paralyzing the sympathetic filaments, contracts the pupil so powerfully, that it may be used to break adhesions which remain after iritis.

The Trochleator, or 4th nerve, is a very fine, long band arising from the roof of the 4th ventricle and the

superior cerebellar peduncles, and distributed to the orbital surface of the superior oblique muscle, which it alone supplies. Sir C. Bell calls it "the respiratory nerve of the eye," and says it is large in all animals capable of much expression. The opthalmic, the sensitive nerve of the eye, and all its appendages, has been already described (p. 347).

The Abducent, or sixth nerve, emerges between the pons and pyramid, and after a very free communication with the sympathetic in the cavernous sinus, supplies alone the external rectus, and is thus purely motor. The nerve has been found injured or compressed in cases of convergent strabismus. The facial nerve will be afterwards described-but it may be here mentioned that it supplies the orbicularis and tensor tarsi muscles, so that division of it is followed by open eye (lagophthalmos), and overflow of tears (stillicidium), and stimulation by spasmodically closed lids (blephrospasmus), and dryness of the eye. The influence of the sympathetic on the movements of the iris and the vascular supply, has been alluded to at page 293.

The Human Eye is almost a globe, its transverse and vertical axes measuring about an inch, and its anteroposterior diameter being 14 lines, owing to the projection of the cornea. Its parts are divisible into-1. Coats, or protective structures; 2. Dioptric media; and 3. Nervous or percipient apparatus. In the annexed representation of a horizontal section of the eye-ball, all the parts are kept proportionably equal.

The Sclerotic is composed of white fibres interwoven in every direction, but leaving a few spaces, probably nutritive, between them, and forms a hollow sphere of such toughness and resistance that it retains its shape when emptied of contents. It is covered anteriorly by the tendinous expansion of the 4 recti (tunica albuginea), which gives it a whiter tint, and thickens it. It is thickest at the entrance of the optic nerve, and thinnest