Muscles of the eye
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Figure 2: Extrinsic muscles of the left eyeball, dorsolateral view.
Source: Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.
Figure 3. Extrinsic muscles of the eye, dorsolateral aspect.
Source: Evans H.E., Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.
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References
Figure 1: Retractor bulbi muscle exposed, lateral view.
Source: Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.
Source: Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.
Figure 3. Extrinsic muscles of the eye, dorsolateral aspect.
Source: Evans H.E., Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.
Figure 4: Extrinsic ocular muscles and their action on the left eyeball.
Source: Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.
Figure 5: Anterior half of the left equine eye, viewed from behind. 1. Lens, 2. Ciliary body, 3. Choroid covered by pigmented outer layer of retina, 3'. Remnants of inner nervous layer of retina which has been removed, 4-7. dorsal, ventral, medial and lateral rectus muscles, 8. dorsal oblique muscle, 9. ventral oblique muscle.
Source: Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.
Figure 6: Ocular muscles. 1. Dorsal oblique m., 2. Dorsal rectus m., 3. Retractor bulbi, 4. Medial rectus m., 5. Optic nerve, 6. Ventral rectus m., 7. Ventral oblique m.
Source: Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.
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Figure 7: Stumps of ocular muscles viewed from behind the left eyeball. 1. Dorsal rectus m., 2. Lateral rectus m., 3. Ventral rectus m., 4. Medial rectus m., 5. Ventral oblique m., 6. Dorsal oblique m., 7. Retractor bulbi, 8. Optic nerve.
Source: Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.
Click HERE to test yourself!!!
Table 1: Summary of external muscles of the eye with corresponding origin, insertion and action.
Muscle
|
Note
|
Origin
|
Insertion
|
Action
|
Dorsal rectus
|
Insert closer to the corneoscleral junction than the retractor muscles
Between the spaces between the rectus muscles, parts of the retractor bulbi can be seen
|
Annulus of Zinn
|
Sclera; near equator of the eyeball; closer to corneosclera junction
|
Rotate globe upward,
Elevates globe
|
Ventral rectus
|
Rotate globe downward,
Depresses globe
| |||
Medial rectus
|
Rotate globe medially
| |||
Lateral rectus
|
Rotate globe laterally
| |||
Dorsal oblique
|
Ascends on the dorsomedial side of the extraocular muscles dorsal to the medial rectus
Narrow muscle that forms a long tendon rostrally that passes through a groove in the trochlea
|
Tendon of the dorsal oblique muscle turns and courses laterally after passing around the trochlea
|
Attaches to the sclera under the tendon of insertion of the dorsal rectus muscle (insertion is difficult to be distinguished unless dissected)
|
Rotate dorsal part of globe medially and ventrally
|
Ventral oblique
|
The only extraocular muscle that does not arise from the apex of the orbit
|
Rostral border of the palatine bone at the level of the maxillary foramen, passes ventral to the ventral rectus
|
Sclera at the insertion of the lateral rectus
|
Rotate ventral part of globe medially and dorsally
|
Retractor bulbi
|
Consists of four fascicles that surround the optic nerve, dorsal pair and ventral pair
|
Lateral margin of the optic canal
|
Sclera
|
Retract globe
|
Levator palpebrae superioris
|
Narrow and superficial
Involved with palpebral fissure |
Begins at the apex of the orbit, extends over the dorsal rectus and widens
|
Insert as a flat tendon in the upper eyelid
|
Raise upper eyelid, retract superior eyelid
|
Orbicularis oculi
|
Involved with palpebral fissure
Most important muscle that closes palpebral fissure Composed of two parts: Pars orbitalis and Pars palpebralis (division is not distinct in dogs) |
Pars palpebralis: Medial palpebral ligament and encircles palpebral fissure
Pars orbitalis: Surrounds the pars palpebralis; ventral component from the medial palpebral ligament and dorsal component decussate with ventral compoent |
Pars palpebralis: Encircles and inserts again to the medial palpebral ligament
Pars orbitalis: ventral component fan out caudally and dorsally to the superficial surface of frontalis muscle Pars palpebralis and orbitalis: form lateral palpebral raphe |
Close palpebral fissure (exerts a sphincterlike action)
|
Retractor anguli oculi
(lateralis) |
Involved with palpebral fissure
Small and flat Paralle and superficial to the lateral palpebral ligament |
Arises from the temporal fascia near the temporo- zygomatic suture
|
Bled in with fascicles of the palpebral part at the lateral commissure of the lid
|
Lengthen lateral palpebral fissure
Close palpebral fissure |
Corrugator supercilli
|
Involved with palpebral fissure
|
Assist in elevating upper eyelid
|
References
- Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.
- Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.
- Evans H.E., Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.
- Maggs D.J., Miller P.E. and Ofri R. (2013) Slatter's fundamentals of veterinary ophthalmology, 5th edn., Missouri: Elsevier.
