Levator Palpebrae. Rectus Internus.
Rectus Superior. Rectus Extcrnus.
Rectus Inferior. Obliquus Superior.
Obliquus Inferior.
Dissection. To open the cavity of the orbit, the skull-cap and brain should be first removed; then saw through the frontal bone at the inner extremity of the supra-orbital ridge, and externally at its junction with the malar. The thin roof of the orbit should then be comminuted by a few slight blows with the hammer, and the superciliary portion of the frontal bone driven forwards by a smart stroke ; but must not be removed. The several fragments may then be detached, when the periosteum of the orbit will be exposed: this being removed, together with the fat which fills the cavity of the orbit, the several muscles of this region can be examined. To facilitate their dissection, the globe of the eye should be distended; this may be effected by puncturing the optic nerve near the eyeball, with a curved needle, and pushing it onwards into the globe. Through this aperture the point of a blow-pipe should be inserted, and a little air forced into the cavity of the eyeball; then apply a ligature around the nerve, so as to prevent the air escaping. The globe should now be drawn forwards, when the muscles will be put upon the stretch.
The Levator Palpebrce is a thin, flat, triangular muscle. It arises from the under surface of the lesser wing of the sphenoid, immediately above the optic foramen; and is inserted, by a broad aponeurosis, into the upper border of the superior tarsal cartilage. At its origin it is narrow and tendinous, but soon becomes broad and fleshy, and finally terminates in a broad aponeurosis.
Relations. By its upper surface, with the frontal nerve and artery, the periosteum of the orbit; and in front with the inner surface of the broad tarsal ligament. By its under surface, with the Superior rectus; and, in the lid, with the conjunctiva.
The Rectus Superior (Attollens), the thinnest and narrowest of the four Recti, arises from the upper margin of the optic foramen, beneath the Levator palpebrae and Superior oblique, and from the fibrous sheath of the optic nerve; and is
inserted, by a tendinous expansion, into the sclerotic coat of the eyeball, about three or four lines from the margin of the cornea.
Relations. By its upper surface, with the Levator palpebrae. By its under surface, with the optic nerve, tho ophthalmic artery, and nasal nerve; and in front with the tendon of the Superior oblique and the globe of the eye.
The Inferior and Internal Recti arise by a common tendon (the ligament of Zinn), which is attached around the circumference of the optic foramen, except at its upper and outer part.
The External rectus has two heads: the upper one arises from the outer margin of the optic foramen, immediately beneath the Superior rectus; the lower head, partly from the ligament of Zinn, and partly from a small pointed process of bone on the lower margin of the sphenoidal fissure. Each muscle passes forward in the position implied by its name, to be inserted, by a tendinous expansion, into the sclerotic coat of the eyeball, about three or four lines from the margin of the cornea. Between the two heads of the External rectus is a narrow interval, through which pass the third, nasal branch of the fifth, and sixth nerves, and the ophthalmic vein. Although nearly all these muscles present a common origin, and are inserted in a similar manner into the sclerotic coat, there are certain differences to be observed in them, as regards their length and breadth. The Internal rectus is the broadest, the External the longest, and the Superior the thinnest and narrowest.
The Superior Oblique is a fusiform muscle, placed at the upper and inner side of the orbit, internal to the Levator palpebrae. It arises about a line above the inner margin of the optic foramen, and, passing forwards to the front and inner side of the orbit, terminates in a rounded tendon, which passes through a fibro-cartilaginous pulley attached to a depression beneath the internal angular process of the frontal bone, the contiguous surfaces of the tendon and pulley being lined by a delicate synovial membrane, and enclosed in a thin fibrous investment. The tendon is then reflected backwards and outwards beneath the Superior rectus to the outer and posterior part of the globe of the eye, and inserted into the sclerotic coat between the Superior and External recti muscles, midway between the cornea and entrance of the optic nerve.
Relations. By its upper surface, with the periosteum covering the roof of the orbit, and the fourth nerve. By its under surface, with the nasal nerve, and the upper border of the Internal rectus muscle.
The Inferior Oblique is a thin, narrow muscle, which arises from a depression in the orbital plate of the superior maxillary bone, immediately external to the lachrymal groove. Passing outwards and backwards beneath the Inferior rectus, it terminates in a tendinous expansion, which is inserted into the outer and posterior part of the sclerotic coat of the eyeball.
Relations, By its superior surface, with the globe of the eye, and with the Inferior rectus. By its under surface, with the periosteum covering the floor of the orbit, and with the External rectus.
Nerves. The Levator palpebrae, Inferior oblique, and all the recti excepting the External, are supplied by the third nerve; the Superior oblique by the fourth; the External rectus by the sixth.
Actions. The Levator palpebrae raises the upper eyelid, and is the direct antagonist of the Orbicularis palpebrarum. The four Recti muscles are attached in such a manner to the globe of the eye, that, acting singly, they will turn it either upwards, downwards, inwards, or outwards, as expressed by their names. If any two Recti act together, they carry the globe of the eye in the diagonal of these directions, viz. upwards and inwards, upwards and outwards, downwards and inwards, or downwards and outwards. By some anatomists, these muscles have been considered the chief agent in adjusting the sight at different distances, by compressing the globe, and so lengthening its antero-posterior diameter. The Oblique are the ' rotatory muscles' of the eyeball. The Superior oblique acting alone, would rotate the globe, so as to carry the pupil outwards and downwards to the lower and outer side of the orbit; the Inferior oblique rotating the globe in such a direction, as to carry the pupil upwards and outwards to the upper and outer angle of the eye.
Surgical Anatomy. The position and exact point of insertion of the tendons of the Internal and External recti muscles into the globe, should be carefully examined from the front of the eyeball, as the surgeon is often required to divide one or the other muscle for the cure of strabismus. In convergent strabismus, which is the most common form of the disease, the eye is turned inwards, requiring the division of the Internal rectus. In the divergent form, which is more rare, the eye is turned outwards, the External rectus being especially implicated. The deformity produced in either case is considerable, and is easily remedied by division of one or the other muscle. This operation is readily effected by having the lids well separated by retractors held by an assistant, and the eyeball being drawn outwards by a blunt hook ; the conjunctiva should be raised by a pair of forceps, and divided immediately beneath the lower border of the tendon of the Internal rectus, a little behind its insertion into the sclerotic ; the submucous areolar tissue is then divided, and into the small aperture thus made a blunt hook is passed upwards between the muscle and the globe, and the tendon of the muscle and conjunctiva covering it divided by a pair of blunt-pointed scissors. Or the tendon may be divided by a sub-conjunctival incision, one blade of the scissors being passed upwards between the tendon and the conjunctiva, and the other between the tendon and sclerotic. The student, when dissecting these muscles, should remove on one side of the subject the conjunctiva from the front of the eye, in order to see more accurately the position of these tendons, and on the opposite side the operation may be performed.
inserted, by a tendinous expansion, into the sclerotic coat of the eyeball, about three or four lines from the margin of the cornea.
Relations. By its upper surface, with the Levator palpebrae. By its under surface, with the optic nerve, tho ophthalmic artery, and nasal nerve; and in front with the tendon of the Superior oblique and the globe of the eye.
The Inferior and Internal Recti arise by a common tendon (the ligament of Zinn), which is attached around the circumference of the optic foramen, except at its upper and outer part.
The External rectus has two heads: the upper one arises from the outer margin of the optic foramen, immediately beneath the Superior rectus; the lower head, partly from the ligament of Zinn, and partly from a small pointed process of bone on the lower margin of the sphenoidal fissure. Each muscle passes forward in the position implied by its name, to be inserted, by a tendinous expansion, into the sclerotic coat of the eyeball, about three or four lines from the margin of the cornea. Between the two heads of the External rectus is a narrow interval, through which pass the third, nasal branch of the fifth, and sixth nerves, and the ophthalmic vein. Although nearly all these muscles present a common origin, and are inserted in a similar manner into the sclerotic coat, there are certain differences to be observed in them, as regards their length and breadth. The Internal rectus is the broadest, the External the longest, and the Superior the thinnest and narrowest.
The Superior Oblique is a fusiform muscle, placed at the upper and inner side of the orbit, internal to the Levator palpebrae. It arises about a line above the inner margin of the optic foramen, and, passing forwards to the front and inner side of the orbit, terminates in a rounded tendon, which passes through a fibro-cartilaginous pulley attached to a depression beneath the internal angular process of the frontal bone, the contiguous surfaces of the tendon and pulley being lined by a delicate synovial membrane, and enclosed in a thin fibrous investment. The tendon is then reflected backwards and outwards beneath the Superior rectus to the outer and posterior part of the globe of the eye, and inserted into the sclerotic coat between the Superior and External recti muscles, midway between the cornea and entrance of the optic nerve.
Relations. By its upper surface, with the periosteum covering the roof of the orbit, and the fourth nerve. By its under surface, with the nasal nerve, and the upper border of the Internal rectus muscle.
The Inferior Oblique is a thin, narrow muscle, which arises from a depression in the orbital plate of the superior maxillary bone, immediately external to the lachrymal groove. Passing outwards and backwards beneath the Inferior rectus, it terminates in a tendinous expansion, which is inserted into the outer and posterior part of the sclerotic coat of the eyeball.
Relations, By its superior surface, with the globe of the eye, and with the Inferior rectus. By its under surface, with the periosteum covering the floor of the orbit, and with the External rectus.
Nerves. The Levator palpebrae, Inferior oblique, and all the recti excepting the External, are supplied by the third nerve; the Superior oblique by the fourth; the External rectus by the sixth.
Actions. The Levator palpebrae raises the upper eyelid, and is the direct antagonist of the Orbicularis palpebrarum. The four Recti muscles are attached in such a manner to the globe of the eye, that, acting singly, they will turn it either upwards, downwards, inwards, or outwards, as expressed by their names. If any two Recti act together, they carry the globe of the eye in the diagonal of these directions, viz. upwards and inwards, upwards and outwards, downwards and inwards, or downwards and outwards. By some anatomists, these muscles have been considered the chief agent in adjusting the sight at different distances, by compressing the globe, and so lengthening its antero-posterior diameter. The Oblique are the ' rotatory muscles' of the eyeball. The Superior oblique acting alone, would rotate the globe, so as to carry the pupil outwards and downwards to the lower and outer side of the orbit; the Inferior oblique rotating the globe in such a direction, as to carry the pupil upwards and outwards to the upper and outer angle of the eye.
Surgical Anatomy. The position and exact point of insertion of the tendons of the Internal and External recti muscles into the globe, should be carefully examined from the front of the eyeball, as the surgeon is often required to divide one or the other muscle for the cure of strabismus. In convergent strabismus, which is the most common form of the disease, the eye is turned inwards, requiring the division of the Internal rectus. In the divergent form, which is more rare, the eye is turned outwards, the External rectus being especially implicated. The deformity produced in either case is considerable, and is easily remedied by division of one or the other muscle. This operation is readily effected by having the lids well separated by retractors held by an assistant, and the eyeball being drawn outwards by a blunt hook ; the conjunctiva should be raised by a pair of forceps, and divided immediately beneath the lower border of the tendon of the Internal rectus, a little behind its insertion into the sclerotic ; the submucous areolar tissue is then divided, and into the small aperture thus made a blunt hook is passed upwards between the muscle and the globe, and the tendon of the muscle and conjunctiva covering it divided by a pair of blunt-pointed scissors. Or the tendon may be divided by a sub-conjunctival incision, one blade of the scissors being passed upwards between the tendon and the conjunctiva, and the other between the tendon and sclerotic. The student, when dissecting these muscles, should remove on one side of the subject the conjunctiva from the front of the eye, in order to see more accurately the position of these tendons, and on the opposite side the operation may be performed.
