GUIDE TO THE HEAD AND NECK i577 



forwards to the sphenoideil fissure. A large portion of the malar bone is to 

 be removed, for which purpose the bone-pliers may suffice. In his further 

 mode of procedure the dissector should be careful to leave intact the portion 

 of bone immediately surrounding the optic foramen. The inner and outer 

 saw-cuts are to be connected by using the chisel and mallet, one or two smart 

 knocks being sufficient for this purpose. Thereafter the osseous roof of the 

 orbit is to be tilted forwards by a smart knock ^^ath the mallet. The small 

 wing of the sphenoid bone is next to be removed with the bone-pliers. In 

 the foregoing manner the cavity of the orbit will be exposed, and the sphenoidal 

 fissure will be opened from above. 



The periosteum of the orbit is to be examined, and then laid open. Exactly 

 in the median line, and embedded in the soft fat of the orbit, the dissector 

 will find the frontal nerve, which anteriorly is accompanied by the supra- 

 orbital artery, and divides into supra-orbital and supra-trochlear. The 

 supratrochlear nerve, before leaving the orbit, will be found to give oflE a 

 small twig, which descends to form a loop with the infratrochlear branch of 

 the nasal nerve. More deeply placed than the frontal nerve, but also in 

 the median line, the levator palpebrae superioris muscle is to be dissected, 

 and immediately beneath it the superior rectus. The branches of the upper 

 division of the third or oculo-motor nerve to these two muscles are to be 

 found entering the deep or ocular surface of each muscle. 



The superior oblique muscle is to be dissected along the inner wall of the 

 orbit, where it lies superficially, and the dissector is to show the fourth nerve 

 entering its superficijd or orbital surface far back. The muscle is to be fol- 

 lowed forwards, and its tendon traced through the trochlea or pulley, and 

 thereafter to its insertion. Underneath the superior oblique muscle will be 

 found the internal rectus, in dissecting which the branch from the lower division 

 of the third nerve is to be shown entering its deep or ocular surface. Between 

 the superior oblique and interned rectus muscles will be found the nasal nerve 

 and the anterior and posterior ethmoidal vessels. The lachrymal gland will 

 be found at the anterior and outer part of the orbit. The lachrymal nerve, 

 accompanied by the lachrymal artery, is to be found along the outer wall 

 of the orbit, and is to be followed forwards to its distribution. A branch is 

 to be looked for passing downwards from the lachrymal nerve to join the 

 temporal branch of the orbital or temporo-malar nerve. Beneath this nerve 

 the dissector will find the external rectus muscle. 



The frontal nerve and levator palpebrae superioris are to be divided, and 

 to facilitate the dissection of the ocular muscles the eyeball may be inflated. 

 This must be done with very great care, in order to leave intact important 

 structures not yet dissected. The optic nerve is to be exposed by carefully 

 pushing aside the jrielding structures which cover it. Having slipped a liga- 

 ture round the nerve not far from the eyebaJl, a puncture is to be made in 

 the nerve behind the ligature, and a blow-pipe is to be pushed into the nerve 

 as far as its centre. The blow-pipe is then to be pushed forwards into the 

 eyeball, and when the eyeball has been inflated through it the pipe is to be 

 withdrawn, and the ligature made fast. It is possible to destroy the ciliary 

 ganglion in inflating the eyeball, but that ganglion could easUy be dissected 

 on the outer side of the optic nerve before taking the steps necessary for 

 inflation. 



In the dissection of the ocular muscles the capsule of Tenon is to be kept 

 in view. It forms a connective-tissue covering for the sclerotic coat of the 

 eyeball, and extends from the point of entrance of the optic nerve to near 

 the margin of the cornea, where it joins the ocular conjunctiva. Between 

 the capsule of Tenon and the sclerotic a space can easily be demonstrated 

 by puncturing the capsule, and introducing the handle of a scalpel. This is 

 the periscl erotic space, or Tenon's space. The suspensory ligament of Lock- 

 wood requires great care in dissection. It is a thickening of the lower part 

 of Tenon's capsule, and extends between the malar and lachrymal bones. 

 The capsule of Tenon is pierced by the ocular muscles, to which it furnishes 

 sheaths. 



In connection with the sheaths of the recti muscles important forward 



