THE ORBITAL FASCIA AND OCULAR MUSCLES 861 



tinuous with the fibrous layer of the fids. Its medial part, which is in contact with 

 the orbital wall, is thin; incorporated with it beneath the root of the supraorbital 

 process is the bar of cartilage around which the superior oblique muscle is reflected. 

 The lateral part is thicker, and is strengthened by an elastic band which is attached 

 to the pterygoid crest and furnishes origin to the thin, unstriped orbital muscle. A 

 quantity of fat (Corpus adiposum extraorbitale) lies about the periorbita, and within 

 it is the intraorbital adipose tissue (Corpus adiposum intraorbitale) which fills the 

 interstices between the eyeball, muscles, etc. 



THE ORBITAL FASCIA AND OCULAR MUSCLES (Figs. 563, 564, 692) 



The straight muscles of the eyeball and the oblique muscles in part are enclosed 

 in fibrous sheaths (Fascise musculares), formed by superficial and deep layers of 

 fascia, which are united by intermuscular septa in the interstices between the 

 muscles. The superficial fascia is thin; it blends in front with the fibrous layer of 

 the eyelids and is attached behind around the optic foramen. The deep fascia 

 consists anteriorly of two layers, one of which is continuous with the fibrous tissue 

 of the lids, while the other is attached at the corneo-scleral junction. 



The posterior part of the eyeball is covered by the fascia bulbi, so that between 

 them a lymph space (Spatium interfasciale) is enclosed which communicates with 

 the subdural space along the course of the optic nerve. 



The levator palpebrae superioris muscle' is a thin band about half an inch in 

 width which lies above the rectus dorsalis. It is narrow at its origin above and 

 behind the ethmoidal foramen and ends by an expanded tendon in the upper lid. 

 Its action is to raise the upper lid. 



The muscles of the eyeball (Mm. oculi) are seven in number — four straight, 

 two oblique, and a retractor. 



The straight muscles (Mm. recti) are designated according to their positions as 

 rectus dorsalis s. superior, rectus ventralis s. inferior, rectus medialis, and rectus 

 lateralis. They are all band-like, arise close together around the optic foramen, 

 and diverge as they pass forward to the eyeball. On reaching the latter they end 

 in thin tendons which are inserted into the sclera in front of the equator of the eye- 

 ball. 



The retractor oculi surrounds the optic nerve, and is incompletely divided into 

 four parts which alternate with the recti. They arise around the optic nerve and 

 are inserted into the sclera behind the recti. 



The obliquus dorsalis s. superior is the longest and narrowest of the ocular mus- 

 cles. It arises near the ethmoidal foramen and passes forward medial to the rectus 

 medialis. Under the root of the supraorbital process it is reflected almost at a 

 right angle around a cartilaginous pulley (trochlea), which is attached to the 

 anterior part of the inner wall of the orbit, a bursa being interposed here. The 

 muscle is then directed outward and somewhat forward, and ends in a thin tendon 

 which passes between the rectus dorsalis and the eyeball, and is inserted into the 

 sclera between the dorsal and lateral recti, about half an inch behind the margin 

 of the cornea. 



The obliquus ventralis s. inferior is wide and much shorter than the recti. 

 It arises from the medial wall of the orbit in the small depression (Fossa muscularis) 

 behind the lacrimal fossa. It curves around the rectus ventralis and is inserted 

 into the sclera near and partly beneath the rectus lateralis. 



Actions. — The dorsal and ventral recti rotate the eyeball about a transverse 

 axis, moving the vertex of the cornea upward and downward respectively.^ Simi- 



1 This belongs to the upper eyelid, but is mentioned here on account of its position and the 

 fact that in dissection it must be dealt with before the muscles of the eyeball. 



2 These terms are used with reference to the axis of the eyeball, not that of the head. 



