1068 



SPECIAL SENSE ORGANS 



and medial edge of the foramen, and extends down and out so as to embrace part of the opening 

 of the superior orbital fissure. Their origins may be said at first to form a short, common, 

 tendinous tube, from which the individual muscles soon separate, taking the positions indicated 

 by their respective names. The lateral rectus has two origins from bone, one on either side of 

 the superior orbital fissure. But in the fresh state the fissure is here bridged across by fibrous 

 tissue, from which this rectus also springs, so that its origin is in reality continuous. The part 

 of this fibrous ring nearest the foramen (corresponding to the origins of the superior and medial 

 recti) is closely connected with the outer sheath of the optic nerve. The remaining two long 

 muscles arise just outside the upper and medial part of the above-mentioned ring, and are often 

 partially united; the levator palpebrse tendon is in close relation to the origin of the superior 

 rectus, while the superior oblique arises from the periosteum of the body of the sphenoid bone 

 one or two millimetres in front of the origin of the medial rectus. 



The four recti muscles lie rather close to the corresponding orbital walls for the first half of 

 their course, the superior rectus, however, being overlapped in part by the levator palpebrie; 

 they then turn toward the eyeball, running obliquely through the orbital fat, and are finally 

 inserted by broad, thin tendons into the sclera in front of the equator. From their respective 

 positions in the orbit, the axis of this cone of muscles is oblique to the antero-posterior axis of 

 the eyeball. The thickest of these muscles is the medial rectus, next the lateral, then the infe- 



FiG. 810. — Dissection of the Left Orbit from in Front. 



Levator palpebrae superioris 



Sclera I 

 Tendon of superior oblique i i Superior rectus 



Lacrimal gland 

 Lateral rectus 



' Cornea 

 Inferior rectus 

 - Orbital adipose 



Medial rectus 



Inferior oblique 



rior, and the superior rectus is the thinnest. As regards length, the muscular belly of the superior 

 rectus has the longest course, and the others diminish in the order — medial, lateral, and inferior 

 rectus. The lateral rectus is supplied by the abducens nerve. The other three recti muscles 

 are all supplied by the oculomotor nerve. 



The levator palpebrae superioris courses along th(^ roof of the orbit close to the poriosteuni 

 for the greater part of its course, partially overlapping the sujierior rectus; it finally descends 

 through the orbital fat, and widens out to be inserted into the root of the upper lid. It may be 

 brieHy described as being inserted in two distinct layers separated by a horizontal interval. 

 The upper or anterior layer of insertion is fibrous, and passes in front of the tarsus, where it comes 

 into relat ion with fil)res of the orbicularis. The lower layer (H)nsists of smooth muscle (Miiller's 

 superior tarsal muscle), and is in.serted along the upper border of the tarsus. The levator has 

 al.so connections with the sheath of the superior rectus. These dilTerent insertions of the muscle 

 will be referred to later along with the (lescrii)tion of the orl)ital fasciie and of the upper eyelid. 

 It gets its nerve supply from the oculomotor ruM've, but the smooth muscle developed in its lower 

 layer of insertion is supplied by the synipathct ic nervous system. As its name expresses, its 

 actiini is to raise the upi)ei lid and to sui)port it whil(> the eye is open. 



The superior oblique runs forward close to the medial part, of the orbital roof until it reaches 

 the fovea trrjchlcaris near tlu^ medial angular i)rocess, where it liecomes tendinous and passes 

 through a fibro-cuf il;i(iinous pulley attached to th(! fovea jnst named. On passing throush 

 this j)ulley, or trochlea, the tendon l)en(ls at an angle of 50°, running posteriorly and lat(!rally 

 under the snperior rectus to its insertion into the sclera. It is siipplied !)y the trochlear nerve. 



The inferior oblique arises from the front of the orbit, about the jun(;tion of its mculial and 

 inf(>rior walls, just lateral to th(> lower end of the lacrimal groove. It runs, in a sloping direction, 

 latepMlly and |)ost(Tiorly, lying at first, between the inferior rectus and the orbit,al floor, then 

 between the lateral rectus and the globe; finally it ascends slightly, to be inserted by a short 



