782 
tremity of the cut nerve produced contraction 
of the pupil, although under the circumstances 
the animal could not have been conscious of 
such irritation. 
Radiated or sympathetic sensations. 
The optic nerve participates in a class of ob- 
scure sensations to which a brief allusion may 
be here permitted ; these are called radiated or 
Sympathetic sensations; they occur occasion- 
ally in health, though they are more frequently 
ptomatic of disease or irritation elsewhere 
situated, and as they are likewise manifested 
by other nerves it would be erroneous to con- 
sider them peculiar to the optic. The pheno- 
mena to which allusion is made are for the 
most part transitory affections of sensitive 
nerves which do not seem to depend on any 
direct impression made upon the nerve af- 
fected, but rather to be | sive te by causes 
which act on other (generally distant) parts of 
the system. 
The following will serve as examples of the 
affections under consideration. 
A discordant sound, such as that produced 
by setting a saw or scratching glass, gives rise 
to shuddering, or a sensation as if water were 
dropping over the surface. Tickling the soles 
of the feet occasions general sensations of the 
most disagreeable nature; and the impression 
of a strong light on the eye is often followed 
by a sense of irritation in the nose, with violent 
sneezing. 
Similar affections of the optic nerve will 
readily occur to the reader’s recollection ; thus 
various forms and degrees of temporary insen- 
sibility or excitement of the retina, which are 
known to depend on gastric disturbance, belong 
to this category, and many other such instances 
might be adduced. 
acts, such as the foregoing, have long been 
familiar to physiologists; but to account for 
them seems still to be a matter of difficulty. 
The supposition that the connections of the 
r domes etic with the nerves affected explain 
e problem is far from satisfactory; the 
most plausible theory is that which supposes 
the primary irritation to be propagated in 
' a centripetal direction along the nerves of the 
part to the cerebro-spinal centres, and thence 
reflected upon the roots of those nerves in 
which the sensations are developed, in some- 
what the same way that excito-motory impres- 
sions on nerves come to produce reflex motions; 
the difference in the two cases amounting to 
this, that in the one the primary impression 
reacts upon motor nerves, giving rise to reflex 
motions, in the other on sensitive nerves causing 
thereby reflex sensations. 
Though this may be the true explanation, it 
is nevertheless not perfectly satisfactory, for it 
does not shew why the reflex irritation should 
be prone to fall on one sensitive nerve in pre- 
ference to another, yet the optic is known in 
such cases to suffer more frequently than the 
auditory or olfactory. 
BIBLIOGRAPHY.—The following books may be 
referred to in addition to the several sytematic 
treatises on Physiology and Descriptive Anatomy. 
Sir J. Newton, his optics, query 15, London, 1718, 
ORBIT. 
John og peeg Fe of nature, translated by 
Thomas Flloyd, 1758. Sam. Thom. ing, De 
basi encephali et originibus neryorum, B.. 
A Monro, The structure and physiology of 
fishes, Edinb, 1785. F. J. Gall et é. Spurzheim, 
Anatomie et physiologie du systéme nerveux, F 
1810. Cuvier, Mémoires servir hi 
et a V’anatomie des mollusques, Paris, 1é 
ilaire, Philosophie anatomiqu 
monstruosités humaines, Paris, 1822. F 
Recherches expérimentales sur les p evés et les 
fonctions du systéme nerveux, Paris, 1 Herber 
Mayo, Anatomical pg amc comme 
taries, second part, July 1823. Wm. HydeWoll 
On semidecussation of the optic nerves, Ph 
phical Transactions, 1824. H, R, A. Serres, J 
tomie comparée du cervean, Paris, 1824. gen 
Journal de physiologie experimentale et pathe 
logique, Paris, 4. Desmoulins et Magendi 
Anatomie des systémes nerveux des animaux ¢ 
vertebrés, Paris, 1825, rederick Tiedemann, ' 
anatomy of the fcetal brain, translated from th 
French by Wm. Bennett, 1826. Miiller, Physiolog 
des Gesichts-sinnes, Leipz. 1826. Joseph Swa: 
demonstration of the nerves of the human body 
London, 1830. Frederici Arnoldi, Icones ne 
capitis, 1834. Catalogue of the physislogseat 
of comparative anatomy in the Museum of 
Royal College of Surgeons, London, 1833 to 
Samuel Solly, The human brain, its configuratio 
structure, &c. London, 1836, Catalogue of tl 
Museum of the Royal Col of Surgeons i 
Ireland, by John Houston, M.D. Dublin, 
Marshall Hali, Lectures on the nervous system ar 
its diseases, London, 1836: also ‘‘ Memoirs on t 
nervous system,” by same. Fr. Leuret, Anaton 
comparée du systéme nerveux, Paris, 1839. H 
Mayo, On the chiasma of the 
London Medical Gazette, November 1841. A: 
Jacob, On paralytic, ne ic, and other 
diseases of Ak eye, Dublin, 1841. John H, Pou 
Observations on the arrangement of the optic ne 
of the loligo, &c. Dublin Journal of | 
Science, 1843. % 
(Robert Mayne. 
ORBIT. ( Orbis, any thing round; Fr. 7 
bite ; Germ. Augenhihle. )—Inthe presentar 
it is intended to describe, first, the bony frat 
work of the orbit; secondly, the contents* ¢ 
orbit in the order in which are exposed 
a dissection from the roof to the floor of the cat 
and, lastly, to give some account of the ai 
of the muscles contained in the orbit and 
serted into the upper lid and globe of the ¢ 
The orbits are two in number, situated a 
anterior and — part of the face. ‘ 
have the form of quadrangular pyramids, 
bases of which are directed forwards an 
wards, the apices backwards and it 
Each orbit-presents for examination’ four ¥ 
four angles, formed by the meeting of the 
a base, and an apex. " 
The superior wall or roof is concave 4 
rected downwards and slightly forward 
chiefly formed by the orbital plate of the 
bone ; at the posterior part to a slight é: 
the lesser wing of the sphenoid. It 
the suture between the orbital 
frontal and the lesser wing of the sphenoii 
anteriorly on the outer side, the lach 
fossa, which receives a gland of the same i 
* The relative anatomy only of these part 
be given in this article, a special description 
Eye and LACHRYMAL ORGANS having 
been given. 4 “* 
* 
piat 
