806 



THE ORGANS OF SENSE. 



the septal artery from the superior labial. The maxillary sinus is partly supplied by the infra- 

 orbital artery, whilst the sphenoidal sinus gets its chief supply from the spheno-palatine artery. 

 The veins form a dense cavernous plexus ; this condition is well seen in the respiratory region, 

 and especially so over the middle and inferior nasal conch ae and on the lower part of the septum. 

 The venous blood is carried in three chief directions, viz., anteriorly into the anterior facial 

 vein, posteriorly into the spheno-palatine vein, and superiorly 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 lamina cribrosa of the ethmoid, and opens either into 

 the venous plexus of the olfactory bulb or directly into one of the veins on the orbital surface of 

 the frontal lobe of the brain.. The lymph, vessels form an irregular network in the superficial 

 part of the mucous membrane, and can be injected from the subdural or subarachnoid cavities. 

 The larger vessels are directed posteriorly towards the choanae, and are collected into two 

 trunks, of which the larger passes to a lymph gland in front of the epistropheus, and the 

 smaller to one or two lymph glands situated near the greater cornu of the hyoid bone. 



The development of the nose is described in the section which deals with 

 " General Embryology " (p. 50). 



OEGANON VISUS. 



OCULUS. 



The bulb of the eye (O.T. eyeball) constitutes the peripheral part of the organ 

 of sight ; associated with it are certain accessory structures, such as the eyelids 

 and the lacrimal apparatus. 



Cornea 



Sinus venosus sclera 1 



Suspensory ligament 

 Len 



Tendon of 

 lateral 

 rectus 



Anterior chamber 



Iris 



-Posterior chamber 

 Ciliary process 

 Spatia zonularia 



Tendon 01 



medial 



rectus 



Vitreous body 



Fovea centralis 



Lamina cribrosa sclerse 

 Arteria centralis retinae 

 Optic nerve 



FIG. 677. DIAGRAM OF A HORIZONTAL SECTION THROUGH LEFT BULBUS OCDLI AND 



OPTIC NERVE ( x 4). 



Bulbus Oculi. Situated in the anterior part of the orbital cavity, the bulb of the 

 eye is protected in front by the eyelids, and is pierced behind by the optic nerve, 

 which ramifies in its innermost tunic, the retina. The tendons of the ocular 

 muscles are attached to the outer surface of the bulb, a short distance in front of 



