A, The skin around the right orbit has been removed to expose the orbicularis oculi muscle. This muscle surrounds the circumference of the orbit and spreads out on the temple and cheek. It has orbital, palpebral, and lacrimal parts. The orbital part of the orbicularis oculi spreads in a wide band around the margin of the orbit. The palpebral part is located in the margins of the eyelids. The orbital part arises from the nasal process of the frontal bone, the frontal process of the maxilla, and the medial palpebral ligament. On the lateral side, it blends with the occipitofrontalis and the corrugator muscles. Many of the upper orbital fibers are inserted into the skin and subcutaneous tissues of the eyebrow. The palpebral part arises from the medial palpebral ligament and the bone above and below the ligament. Some of its fibers lie close to the margin of the eyelid behind the eyelashes. The lacrimal part extends behind the lacrimal sac and attaches to the lacrimal bone. The orbicularis oculi is the sphincter muscle of the eyelids. The palpebral portion closes the eyelids. The actions of the lacrimal part are important in tear transport. B, The orbicular muscle has been removed to expose the upper and lower tarsi, thin plates of dense fibrous tissue situated deep to the palpebral part of the orbicularis oculi muscle. The tarsi are placed in and give support and shape to each eyelid. Some of the fibers of the levator muscle are attached to the upper tarsus. The medial ends of the tarsi are attached by a tendinous band, the medial canthal ligament, to the upper part of the lacrimal crest and the adjoining part of the frontal process of the maxilla in front of the lacrimal crest. The lateral ends of the tarsi are attached by a band, the lateral canthal ligament, to a tubercle on the zygomatic bone immediately within the orbital margin. The orbital septum that separates the facial from the orbital structures has been removed. It attaches to the orbital margin where it is continuous with the periosteum along the anterior edge of the orbit. In the upper eyelid it blends with the superficial part of the aponeurosis of the superior levator, and in the lower eyelid, it blends with the anterior surface of the tarsus. C, The globe and the optic nerve are sur-rounded by the four rectus, the levator, and two oblique muscles. The four rectus muscles arise from the annular tendon that surrounds the optic canal and adjunct part of the superior orbital fissure. The levator muscle arises from the lesser wing of the sphenoid above and anterior to the optic canal and fans out to have a broad attachment to the superior tarsus and the skin of the upper lid. The superior oblique muscle arises from the body of the sphenoid superomedial to the optic canal. The inferior oblique muscle arises from the orbital surface of the maxilla lateral to the nasolacrimal groove. The medial and lateral cheek ligaments (not shown) are fibrous expansions extending from sheaths of the lateral and medial rectus muscles that attach to the zygomatic and lacrimal bone, respectively, and limit the actions of the lateral and medial rectus muscles. D, Globe depressed to show the insertion of the superior rectus muscle and the trochlea and distal tendon of the superior oblique muscle. The superior rectus muscle arises from the annular tendon, passes forward, and attaches to the sclera posterior to the margin of the cornea. The superior oblique muscle arises from the periorbita covering the body of the sphenoid bone superomedial to the optic canal and runs forward, ending in a tendon that loops through the trochlea, a round tendon that attaches to the trochlear fossa of the frontal bone. After looping through the trochlea, the tendon passes laterally and posteriorly below the superior rectus muscle to insert on the sclera between the superior and lateral rectus muscles. E, Globe adducted to show the insertion of the lateral rectus muscle. The lateral rectus muscle arises from the annular tendon and adjacent part of the greater wing of the sphenoid bone and has a vertical line of attachment to the sclera. F, Globe positioned to show the relationship of the inferior rectus and inferior oblique muscles. The inferior rectus muscle arises from the annular tendon and has an oblique line of attachment, with the medial side slightly anterior to the lateral side of the attachment. The inferior oblique muscle arises from the part of the orbital floor formed by the orbital surface of the maxilla in the area just lateral to the nasolacrimal duct, not from the orbital apex, and runs laterally and posteriorly, passing between the inferior rectus muscle and the orbital floor, and then between the lateral rectus muscle and the globe, to insert into the sclera between the superior and lateral rectus muscles near the insertion of the superior oblique muscle. (Images courtesy of AL Rhoton, Jr.)