REGION OF THE EYE. 75 



insertion of the recti muscles on their under (inner) side, passes over the globe poste- 

 riorly, over the optic nerve, and blends with the layer covering the deep surface of the 

 muscles. It is joined to the sclerotic coat of the eye and dural sheath of the nerve 

 by a loose net-work of delicate fibrils. This forms practically a space lined with 

 endothelial plates, similar to the subarachnoid space in the brain. The capsule of 

 Tenon is a distinct, well marked membrane, and the eyeball lies loose and revolves 

 freely within it. It is this space into which the strabismus hook is put when it is 

 desired to cut the recti muscles for squint. Fibrous prolongations are also sent 

 to the sides of the orbit from the internal and external recti muscles. They are 

 the check ligaments; and one from the inferior rectus forms the suspensory ligament 

 of the eye. 



Affections of the Orbit. The orbit is often invaded by tumors, pus, hemor- 

 rhages, and air (producing emphysema). 



Tumors may either originate in the orbital contents, as sarcomas of the lach- 

 rymal gland or eye, or they may come from surrounding regions. It is more rare 

 for them to enter through the natural openings of the orbit than it is for them to 

 push through its thin walls. Coming through natural openings, they may make 

 their entrance : (i) from the brain through the optic foramen or sphenoidal fissure ; 



(2) from the region of the zygomatic and temporal fossae through the sphenomaxil- 

 lary fissure ; (3) from the nasal cavities 



(as I have seen), coming up the lachry- 

 monasal canal. 



In invading the orbit through its walls 

 they may come: (i) from the nasal cavi- 

 ties and ethmoidal cells, pushing through 

 the thin internal wall ; (2) from the frontal 

 sinus, appearing at the upper inner angle; 



(3) from the sphenoidal cells at the pos- 

 terior portion of the inner wall ; (4) from 

 the brain cavity above, breaking through 

 the roof ; (5) from the maxillary sinus 

 below, pushing through the floor. 



Demwids. In the fcetUS, thefrontO- Fig. 89. Dermoid of orbit. Boy, 15 years of age. It 



i < i j extended back to the body of the sphenoid bone. Case of 



nasal process comes from above down- Dr. wm. zentmayer. 

 ward to join the maxillary processes on 



each side. This leaves an orbitonasal cleft to form the orbit. Owing to defects in the 

 development of this cleft, dermoid tumors may occur in its course. They are seen 

 either at the outer or inner angle of the eye. They are more common at the outer 

 angle near the external angular process, and may have a prolongation to the dura 

 mater. They also occur at the inner angle at the frontonasal suture (Fig. 89). At 

 this point, also, meningoceles are liable to occur. As pointed out by J. Bland Sutton 

 the question of diagnosis is of importance, as an attempt to remove a meningocele 

 by operation is apt to be followed by death, whereas a dermoid, though it may have 

 a fibrous prolongation to the dura mater, can be more safely removed. 



Orbital Abscess. Suppuration may either originate within the orbit or extend 

 into it from the neighboring tissues. If the former is the case, it may occur from 

 caries of the bones of the orbit, as in syphilis. It may originate from erysipelas 

 involving the orbit. General inflammation and suppuration of the eye may break 

 through the eye and spread in the orbital tissues (panophthalmitis). If pus enters 

 the orbit from the outside, it is usually from suppuration and caries of the frontal 

 sinus and ethmoidal cells. In this case, the swelling shows itself at the upper 

 portion of the inner angle of the eye. Pus in the maxillary sinus is most apt to 

 discharge into the nose, and not break through the roof into the orbit above. 

 Pus within the orbit tends to push the eyeball forward and even distend the lids. 

 As the orbitotarsal ligament runs from the bony edge of the orbit to the lids, pus 

 does not find an easy exit. The abscess should be opened by elevating the upper 

 lid, and incising the conjunctiva in the sulcus between the globe of the eye and the lid. 

 Pus from suppuration of the lachrymal sac does not tend to invade the orbit but 

 works its way forward to the skin. 



