= Solution
\b[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.<Dissection of the Orbit by Loyola University Chicago>[Step 1, dorsal approach: removal of the roof, preservation of the medial ethmoidal structures, and gentle removal of fat]{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.<Lab Manual - Eye by Texas Tech University Health Sciences Center El Paso>[Procedure 6 and opening of procedure 7: superficial nerves, superior ophthalmic vein, and reflection of levator and superior rectus]{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.<Reflection of the orbital muscles by Texas Tech University Health Sciences Center El Paso>[Procedure 7 commentary: reflect the levator and superior rectus at their mid-bellies and identify the superior division of III; levator attachment is detailed in the anatomy tables]{ref}<Anatomy Tables - Muscles of the Head and Neck by Texas Tech University Health Sciences Center El Paso>[Levator palpebrae superioris row, insertion]{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>.<Anatomy Tables - Muscles of the Head and Neck by Texas Tech University Health Sciences Center El Paso>[Rows for rectus and oblique muscles: origins, insertions, and the superior oblique pulley]{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.<Dissector Answers - Eye by Texas Tech University Health Sciences Center El Paso>[Learning objective 3: rectus and oblique actions and clinical testing positions]{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.<Anatomy Tables - Eye by Texas Tech University Health Sciences Center El Paso>[Nerves table: optic, nasociliary, long ciliary, ethmoidal, ciliary ganglion and short ciliary entries]{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>. \b[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.<Anatomy Tables - Eye by Texas Tech University Health Sciences Center El Paso>[Nerves table: oculomotor and nerve to inferior oblique entries; ciliary ganglion and short ciliary entries distinguish the three fibre components]{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. https://pubmed.ncbi.nlm.nih.gov/6507890/[Variability in relationships of arteries and nerves in the human orbit (1984), abstract: direct dissections found an inferior ophthalmic-artery crossing in some orbits]{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>.<Lab 27: Dissection: Orbit and Ear by Washington State University>[Dissection section, ophthalmic artery and superior ophthalmic vein; branching pattern is variable]{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.
Back to article page
