CEREBRAL SIGHT. 401 



cavity of the nose. From this it is removed by evaporation, the current 

 of air alternately introduced and expired affording the means of accom- 

 plishing that object in a remarkable manner. But should the secretion 

 of water from the lachrymal gland become excessive, as in weeping, this 

 draining mechanism is insufficient, and the water is discharged as tears 

 down the cheek. 



Of the muscles for the 'movement of the eye, the description has, in 

 part, been given under that of the nerves. It may, how- Motions of the 

 ever, be here remarked that the eyeball is moved by six eyeball, 

 muscles, the four straight and the two oblique. The straight muscles 

 arise at the optic foramen, and are inserted into the sclerotic in the four 

 quadrantal positions above, below, right, and left. The action of each 

 of these muscles is to turn the eyeball toward itself; when they contract 

 all together, they fix it. The superior oblique muscle arises from the 

 same place, passes through a pulley beneath the internal angular process 

 of the frontal bone, its tendon being inserted into the sclerotic near to 

 the entrance of the optic nerve. The inferior oblique rises from the in- 

 ner margin of the superior maxillary bone, passes beneath the inferior 

 straight muscle, and is inserted into the sclerotic on its outer and pos- 

 terior part, near the entrance of the optic nerve. The superior oblique 

 rolls the globe inward and forward, the inferior rolls it outward and back- 

 ward ; acting together, they draw the globe forward and converge the 

 axes of the eyes. The nervous supply for these various muscles has al- 

 ready been specified in page 334. 



CHAPTEE XXI. 



OF CEREBRAL SIGHT OR INVERSE VISION. 



Difference, between ordinary Vision and cerebral Sight. Inverse Vision depends on the Vestiges 

 of Impressions existing in the Brain. 



Condition of our perceiving these Impressions is that they must be equal in Intensity to present 

 Sensations. Two Methods of accomplishing this Equalization: 1st, by re-enforcing the old Im- 

 pressions ; 2d, by diminishing the present Sensations. 



Emergence of old Impressions in Sleep, Fever, Death. Artificial Emergence of such Vestiges by 

 Protoxide of Nitrogen, Opium, etc. 



Cerebral Sight used tekologically to indicate the Immortality of the Soul. 



THE perception of external objects depends on the rays of light enter- 

 ing the eye, and converging so as to produce images which make an im- 

 pression on the retina, and, through the optic nerve, are recognized by 

 the brain. The direction of the influences, so far as the observer is con- 

 cerned, is from without to within, from the object to the brain. 



Cc 



