112 



TOPOGRAPHICAL ANATOMY OF THE 



and very slightly forwards, so that its thin tendon, insinuating itself 

 between the superior rectus and the eyeball, is finally inserted into the 

 sclera between the superior and lateral recti muscles. A small synovial 

 bursa surrounds the muscle as it plays through the trochlea. 



Mm. recti (jculi. — The four straight muscles of the eyeball, 

 namely, superior, inferior, medial and lateral, all arise in the neigh- 

 bourhood of the optic foramen, and pass forwards to be inserted by 

 thin tendons into the sclera of the eyeball in front of the equator. 



M. OBLIQUUS INFERIOR. — The inferior oblique ditfers from all the 

 other ocular muscles in that its origin is from the anterior part of 



M. rectus superior. 

 M. obliquus superior., 



M. rectus lateralis. 



M. obliquus inferior 



M. rectus medialis. 



M. retractor oculi. 



M. rectus inferior. 



Fig. 47. — Diagram of the front of the right eyeball to show the 

 insertions of the muscles. 



the orbit. It is also broader than the others, and much shorter. Its 

 origin is from a depression in the lachrymal bone just behind the 

 lachrymal fossa. From this point the muscle passes outAvards under 

 (ventral to) the inferior rectus, and is inserted into the sclera beneath 

 the tendon of the lateral rectus. 



M. RETRACTOR OCULI. — Composed of a variable number of indistinctly 

 separated parts, which all arise from the margin of the optic foramen, the 

 retractor of the eyeball lies within the straight muscles, and is inserted 

 into the sclera immediately behind them. 



N. TROCHLEARis. — The trochlear or fourth cerebral nerve, purely 

 motor in function, leaves the cranium by the trochlear foramen and 

 runs forwards on the surface of the superior oblique muscle, into which 

 it sinks about midway between the ethmoidal foramen and the trochlea 

 through which the muscle plays. 



N. NASOCiLiARis. — The naso-ciliary nerve, a branch of the 

 ophthalmic, should be found at the apex of the orbit between the 



