32 ANATOMY OF THE HEAD AND NECK. 



the long ciliary arteries. The arleria centralis retinae is a 

 very small branch which perforates 'the optic nerve, and is 

 distributed to the interior of the eyeball. 



The dissection of these arteries will have in a measure 

 effected the dissection of the muscles of the orbit. 



The LEVATOR PALPEBR^E is the most superficial of the 

 orbital muscles ; it arises from the roof of the orbit in front 

 of the optic foramen and is inserted by a broad tendon into 

 the tarsal cartilage of the upper eyelid. 



This muscle is to be divided, and its two ends are to be reflected. 



Four straight muscles surround the optic nerve, and are 

 named from their position SUPERIOR and INFERIOR, EX- 

 TERNAL and INTERNAL RECTI MUSCLES ; with the exception 

 of the external rectus, they arise posteriorly from the cir- 

 cumference of the optfc foramen and sheath of the optic 

 nerve by a common attachment ; the external rectus arises 

 by two heads, the upper one joining the superior rectus, 

 and the lower the inferior rectus, springing also from the 

 lower border of the sphenoidal fissure ; between these 

 origins pass the motor oculi (third), the abducens (sixth), 

 and the nasal branch of the ophthalmic nerve, to enter the 

 orbit. The recti muscles are all inserted, at equi-distant 

 intervals, into the sclerotic coat of the eyeball, about a 

 quarter of an inch from the cornea. 



The SUPERIOR OBLIQUE MUSCLE, situated in the upper 

 and inner part of the orbit, is a small rounded muscle 

 arising from the inner side of the optic foramen ; it ends 

 anteriorly in a tendon which passes through a loop attached 

 to a depression in the frontal bone at the inner part of 

 the orbit, and is thence reflected backward and outward, 

 between the globe of the eye and the belly of the superior 

 rectus, to be inserted by a broad and flat tendon into the 

 sclerotic, between the superior and external recti muscles. 

 From this pulley-like peculiarity the superior oblique is 

 sometimes called the trochlearis muscle. The loop is a 

 fibro-cartilaginous ring about an eighth of an inch in width, 

 and, as well as the tendon which plays through it, is lined 

 with a sjmovial membrane. 



In order to examine the next muscle, the optic nerve and the recti 

 muscles must be divided near their origin, and the eye gently turned 

 out of its socket, so as to expose its inferior surface. 



The INFERIOR OBLIQUE MUSCLE arises from the superior 

 maxillary bone, between the margin of the orbit and the 



