THE EYE. 681 
and is continuous with a fibril of the olfactory nerve. Each of these nerve fibrils 
probably retains its independence from its point of origin in an olfactory cell to its 
termination in the olfactory bulb, in the glomerular layer of which it forms a free 
arborisation. 
3. Basal Cells.—These cells are branched, and lie on a basement membrane 
between the deep extremities of the supporting and olfactory cells. 
Olfactory Nerves.—These nerves traverse the cribriform plate of the ethmoid 
bone, and are at first lodged in the bony canals or grooves situated on the inner 
and outer walls of the olfactory area, and, reaching the deep surface of the mucous 
membrane, are continued into the central processes of the olfactory cells. The 
olfactory nerves possess no medullary sheath. 
The fifth cranial nerve supplies branches of ordinary sensation to the nasal mucous membrane 
as follows: The septum is chiefly supplied by the naso-palatine nerve, but its posterior part 
receives some filaments from Meckel’s ganghon and the Vidian nerve, and its anterior portion 
from the nasal branch of the ophthalmic. The outer wall is supplied—(1) by the upper nasal 
branches of the Vidian nerve and Meckel’s ganglion ; (2) by the lower nasal branches derived from 
the anterior palatine; and in front by (8) the outer division of the nasal branch of the ophthalmic. 
The floor and anterior part of the inferior meatus are suppled by a nasal branch of the anterior 
superior dental nerve. 
Blood-vessels.—Arteries. The chief artery of the nose is the spheno-palatine branch of the 
internal maxillary artery. This reaches the nasal cavity through the spheno-palatine foramen, and 
divides into—(a) posterior nasal, which ramifies over the turbinated bones and sends branches to 
the antrum and to the frontal and ethmoidal cells; and (>) naso-palatine, the artery of the 
septum. Twigs are given to the upper portion of the cavity by the anterior and posterior 
ethmoidal arteries, while its posterior part receives some small branches from the descending 
palatine vessel. The nostrils are supplied by the lateral nasal branch of the facial, and by the 
septal artery of the superior coronary. The antrum is partly supplied by the infraorbital artery, 
whilst the sphenoidal sinus gets its chief supply from the pterygo-palatine vessel. The veins 
form a dense plexus almost resembling cavernous tissue in structure. This condition is well seen 
in the respiratory region, and especially so over the middle and inferior turbinated bones and on 
the lower part of the septum. The venous blood is carried in three chief directions, viz. 
forwards into the facial vein, backwards into the spheno-palatine vein, and upwards into the 
ethmoidal veins. The ethmoidal veins communicate with the ophthalmic veins and the veins of 
the dura mater; further, an ethmoidal vein passes up through the cribriform plate of the 
ethmoid, and either opens into the venous plexus of the olfactory bulb or directly into one of the 
veins of the orbital part of the frontal lobe of the brain. The lymphatics form an irregular net- 
work in the superficial part of the mucous membrane, and can be injected from the subdural or 
subarachnoid space. The larger vessels are directed backwards towards the choanz and are 
collected into two trunks, of which the larger passes to a lymphatic gland in front of the 
axis vertebra and the smaller to one or two glands situated near the great cornu of the hyoid 
bone. 
The development of the nose is described in the section which deals with 
“General Embryology ” (p. 36). 
THE KYE. 
The eyeball or globe of the eye (bulbus oculi) constitutes the chief part of the 
organ of sight (organon visus); but, associated with its description, certain 
accessory structures, such as the eyelids and the lachrymal apparatus, fall to be 
considered. 
THE EYEBALL. 
Situated in the anterior part of the orbital cavity, the eyeball is protected in 
front by the eyelids and by their mucous lining, the conjunctiva, and is pierced 
behind by the optic nerve, or nerve of sight, which spreads out to form its innermost 
tunic, the retina. The tendons of the ocular muscles are attached to its outer 
surface a short distance in front of its equator, while its posterior two-thirds are 
enveloped by a loose membrane, termed the capsule of Tenon, or fascia bulbi, which 
separates it from the surrounding orbital fat. 
The eyeball is not quite spherical, being composed of the segments of two 
spheres, viz. an anterior, transparent, corneal segment, possessing a radius of 7 or 
8 mm., and a posterior, opaque, scleral segment, with a radius of about 12 mm. 
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