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The ciliary muscle forms a ring within the anterior ciliary body, deep to the sclera and outside the zonular attachment system of the crystalline lens. Its arrangement connects an anterior scleral attachment to posterior and inward parts of the uveal tissues, allowing contraction to alter zonular tension.

In a meridional section, the anterior ciliary region lies just behind the corneoscleral junction. The scleral spur gives attachment to anterior longitudinal muscle fibres. Posteriorly these fibres extend towards the choroid and its supporting tissues. Between the sclera outside and the ciliary processes inside, oblique or radial and circularly oriented smooth-muscle bundles complete the muscular mass. These fibre directions are regions of one coordinated smooth muscle, not three independently attached external ocular muscles.^[ref]

The ciliary processes project inward from the anterior folded part of the ciliary body, behind the root of the iris and peripheral to the lens equator. Ciliary epithelium covers them; their vascular core and epithelial functions are distinct from the smooth-muscle bundles. The posterior, flatter ciliary region continues towards the ora serrata, where the sensory retina ends. The ciliary body is therefore continuous with choroid posteriorly and related to iris anteriorly, while remaining a separately describable region.

Zonular fibres pass from the ciliary region to the capsule around the equator of the crystalline lens. They cross the circumlental space; the ciliary muscle does not insert directly into the transparent lens substance. The posterior chamber lies behind the iris and in front of the lens and zonular apparatus, and communicates with the anterior chamber through the pupil. The vitreous body lies behind the lens and has its own relation to the posterior zonular region. These spaces must not be drawn as one cavity containing the muscle freely suspended in aqueous fluid.

For near ocular accommodation, contraction reduces the effective diameter of the ciliary ring and changes its position, reducing the zonular forces that flatten the lens. The elastic capsule and lens substance then permit a rounder lens with greater optical power. For distant viewing, relaxation restores greater flattening tension and lower power. Thus ciliary contraction increases lens curvature by relieving a restraint; it does not pull the lens flatter. The conventional mechanism is supported by observations of lens shape and optical changes during accommodation.^[ref]

Parasympathetic motor fibres reach the muscle through the oculomotor nerve, ciliary ganglion and short ciliary nerves. This motor pathway is distinct from the sensory visual input that initiates a near response. Changes in pupil size and convergence often accompany accommodation, but neither should be substituted for an observed change of lens power. With age, reduced lens deformability can impair near focus even though ciliary contraction still occurs. The sketch shows spatial relationships and the direction of the conventional mechanism, rather than a scale drawing or a claim that every historical theory of accommodation was correct.

Expose the orbit (anatomy) in layers, preserving the eye, extraocular muscles, nerves and blood vessels so that their relations can be demonstrated. This is a general explanation of the practical exercise, using present-day anatomy terminology. It does not assert findings in the individual head supplied in 1867. The essential result is an intelligible dissection, with structures traced to their attachments or continuations, rather than a collection of detached parts.

Begin by orienting the head and choosing a superior approach through the anterior cranial fossa. Useful apparatus consists of a small saw or bone-cutting forceps, a fine chisel, fine scissors, dissecting forceps and a blunt probe. The coarse instruments remove bone; the fine instruments separate connective tissue. Remove the dura mater from the orbital part of the frontal bone, then carefully remove the roof of the orbit (anatomy) while leaving the periorbita intact. Extend the exposure towards the apex without driving the instrument into the optic canal or the superior orbital fissure. Preserve the delicate medial wall and its anterior ethmoidal nerve, posterior ethmoidal nerve and accompanying blood vessels. Open the periorbita under direct vision. This establishes a continuous view from the anterior margin towards the apex.^[ref]

In the superficial plane, identify the frontal nerve above the levator palpebrae superioris, and follow its division into the supraorbital nerve and supratrochlear nerve. On the lateral side identify the lacrimal gland, lacrimal nerve and accompanying lacrimal artery. On the medial side find the superior oblique muscle and the trochlear nerve entering it. Separate small amounts of adipose tissue with a blunt probe instead of stripping out the contents in a single mass. Preserve the superior ophthalmic vein where recognizable. Before reflecting any structure, show its course in place: removal of an overlying structure should answer a particular question about what lies underneath it.^[ref]

Next isolate the levator palpebrae superioris and trace it forward towards the upper eyelid. Its expanded tendon reaches the upper tarsal plate and adjacent eyelid tissues; distinguish this from an attachment to the sclera. Divide the levator palpebrae superioris across its belly and reflect the ends, keeping its oculomotor nerve supply attached where practicable. The superior rectus muscle is now exposed. Isolate and reflect it in turn, preserving the superior division of the oculomotor nerve entering the deep surface. This successive exposure demonstrates why the superficial frontal nerve should be located before either muscle is divided.^[ref][ref]

Trace the four rectus extraocular muscles from the common tendinous ring at the apex to the anterior sclera, behind the margin of the cornea. Demonstrate the medial rectus muscle and lateral rectus muscle along the corresponding sides of the eye, and the inferior rectus muscle below it. Trace the superior oblique muscle forwards to the trochlea of superior oblique; its tendon turns backwards and laterally beneath the superior rectus muscle to reach the sclera behind the equator of the eye. The inferior oblique muscle is the important exception to an apical origin: it begins on the anterior medial orbital floor of the maxilla, lateral to the lacrimal sac, and passes backwards and laterally beneath the inferior rectus muscle to the posterior lateral sclera.^[ref]

The following functional explanation makes the muscle display meaningful. The medial rectus muscle produces adduction of the eye, and the lateral rectus muscle produces abduction of the eye. The superior rectus muscle elevates and the inferior rectus muscle depresses, with additional adduction of the eye; the superior rectus muscle also produces intorsion of the eye, and the inferior rectus muscle produces extorsion of the eye. The superior oblique muscle produces intorsion of the eye, depression and abduction of the eye; the inferior oblique muscle produces extorsion of the eye, elevation and abduction of the eye. Depression by the superior oblique muscle is demonstrated most clearly with the eye adducted. Gentle traction on an isolated tendon, with the eye supported, can illustrate its line of pull in the preparation. This mechanical demonstration does not test living nerve function, and no observed movement in the historical specimen is supplied.^[ref]

In the deeper plane, identify the optic nerve entering the posterior eye and trace it back to the optic canal. Identify the nasociliary nerve crossing above it towards the medial wall; follow the long ciliary nerves towards the eye and the anterior ethmoidal nerve and posterior ethmoidal nerve towards the medial bone. On the lateral side of the optic nerve, between it and the lateral rectus muscle, seek the small ciliary ganglion. Preserve the short ciliary nerves that pass from its anterior aspect to the eye; an indiscriminate sweep through the surrounding adipose tissue would destroy precisely these small connections.^[ref]

Trace the inferior division of the oculomotor nerve towards the medial rectus muscle, inferior rectus muscle and inferior oblique muscle, including its connection to the ciliary ganglion. Trace the abducens nerve to the deep surface of the lateral rectus muscle, and the trochlear nerve to the superior oblique muscle. The lateral rectus muscle receives the abducens nerve, the superior oblique muscle receives the trochlear nerve, and the remaining listed extraocular muscles receive the oculomotor nerve. The ciliary ganglion is a relay for fibres of the parasympathetic nervous system carried with the oculomotor nerve towards the sphincter pupillae muscle and ciliary muscle. Sensory fibres connected with the nasociliary nerve, and already postganglionic fibres of the sympathetic nervous system, traverse the ciliary ganglion without another relay.^[ref]

Trace the ophthalmic artery from the optic canal and its continuity with the internal carotid artery, distinguishing it from the optic nerve. Follow recognizable branches: the central retinal artery towards and into the optic nerve, the posterior ciliary arteries towards the posterior sclera, the lacrimal artery towards the lacrimal gland, and the supraorbital artery, anterior ethmoidal artery and posterior ethmoidal artery towards their exits. The usual ophthalmic artery crosses above the optic nerve to reach the medial side, but an individual course must be established by tracing, not imposed on the preparation. ^[ref] Follow the superior ophthalmic vein towards the superior orbital fissure and cavernous sinus. The inferior ophthalmic vein also has communications towards the pterygoid plexus through the inferior orbital fissure.^[ref]

Finally, show the relations at the apex. The optic nerve and ophthalmic artery pass through the optic canal within the common tendinous ring. The divisions of the oculomotor nerve, nasociliary nerve and abducens nerve enter through the part of the superior orbital fissure enclosed by the common tendinous ring; the frontal nerve, lacrimal nerve and trochlear nerve enter outside it. Keep the eye attached until these relations have been displayed. A final labelled account should distinguish structures actually preserved from structures damaged or too small to demonstrate. That qualification matters in a practical dissection: an expected structure is a guide to search, not an observation.

Let an upward force $P$ act along $x=0$ and a downward parallel force $Q$ along $x=d>0$. An equivalent resultant force must preserve both total force and torque. Its signed vertical component is $R=P-Q$, and taking torques about the first line gives $R{x}_R=-Qd$. ThusIts magnitude is $|P-Q|$ and its direction agrees with the larger force. Its line lies outside the two original lines on the side of that larger force; for example, $P>Q$ gives $x_R<0$. The products of the original forces and their perpendicular distances from this line are equal.

If $P=Q\ne 0$ and $d\ne 0$, the total force vanishes but the torque is $-Pd$. No single force is equivalent to this system: it is a force couple of magnitude $Pd$. Its torque is independent of the reference point because translating that point changes the torque by the cross product of the shift and the zero resultant force. Equal opposite forces on the same line instead cancel completely.

The eye is rotated by six extraocular muscles. The rectus muscles approach it from behind; the oblique muscles have oblique lines of pull, with the superior oblique muscle tendon redirected by an orbital pulley. Attachments on the sclera give lever arms about the rotation centre. In the straight-ahead position their actions are as follows; vertical and torsional contributions vary with gaze direction.^[ref]

Coordinated contraction selects the desired rotation and balances unwanted components. This illustrates torque control; the full ocular geometry is not simply the parallel-force pair of the first calculation.