CAVITY OF THE OB JUT 



S55 



are arranged in opponent pairs, viz. superior and inferior recti, superior and 

 inferior obliques, external and internal recti. With the excej.tion oi the short 

 inferidi- ohliiiuc they all arise from th<- liack of the orhit along with the seventh 

 orhital muscle, the elevator of the upper lid. All these hmg niuseles take tlieir 

 origin from the periosteum in the viciinty of the <i])tic foramen. The f(nir recti 

 muscles arise from a tihrous ring, which arches close over the ujtper and inner edge 

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

 the sphenoidal fissure. Their origins may be said at first to form a short, com- 

 mon, tendinous tube, from which the individual muscles soon separate, taking 

 the positions indicated by their respective names. The external rectus has two 

 origins from bone, one on either side of the sphenoidal fissure. But in the fresli 

 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 



Fio 43-3.— Section through Contexts of Khjht Orbit 8-11 mm. behixd the Eyeball, 

 VIEWED FROM BEHIXD. (After Lauj^e.) 



SUPRA OR RITAL 

 NERVE 



Supraoibilal artery 



Levator palpebrae 

 Buperiori3 ruuucle 



Superior 

 rectus muscle 



LAr/finMAL 



SERVE 

 Lachrymal ardry 



— Lachrymal vein 

 Ojjhthal/iiic vein 



Nasn-fronlid 

 artery 



OPTIC NER VE 



Ciliary arterii 

 Central retinal 

 artery 

 Ciliary artery 



Inferior rectus 

 muscle 



Ciliary artery 



External rectus 

 muscle 



(iiiury artery 



— Tllinn SERVE 

 {ERA sen W 

 ISFERIOR 

 ORLiqiE 

 ML.SCLE) 



ring nearest the foramen (corresponding to the origins of the superior and internal 

 recti) is closely connected with the outer sheath of the optic nerve. The remain- 

 ing two long muscles arise just outside the upper and inner part of the above- 

 mentioned ring, and are often partially united; the levator palpe])rte tendon is in 

 close relation to the origin of the superior rectus, while the superior ol)li<iue arises 

 from the perio.steum of the body of the sphenoid bone one or two millimetres in 

 front of the origin of the internal 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 jiart by 

 the levator palpebra:*; they then turn towards the eyeball, running obli(|Uely 

 through the orbital fat, and are finally inserted by broad, thin tendons into the 

 sclerotic in front of the equator. The thickest of these muscles is the internal 

 rectus, next the external, then the inferior, and the superior rectus is the thinnest. 



