Biology of Man 505 



central nervous system to be interpreted (Fig. 246) . Special sense organs 

 in the muscles, called muscle spindles, originate the so-called muscle sense 

 to tell the degree of contraction or the general condition of the muscles. 



The human taste buds are the end organs of nerve filaments arising 

 from the trigeminal, facial, and glossopharyngeal nerves (cranial nerves). 

 The taste organs are located chiefly on the tongue, but also on the palate, 

 epiglottis, and even vocal folds (Fig. 234). The human auditory ap- 

 paratus (Fig. 250) consists of (1) an external ear with its auditory canal 

 with a membranous tympanum (eardrum) at its inner end; (2) the 

 middle ear with its Eustachian tube connecting it with the pharynx to 

 equalize air pressure; the middle ear bones — ham,mer or malleus) (L. 

 malleus, hammer), anvil or incus (L. incus, anvil), and the stirrup or 

 stapes (L. stapes, stirrup) ; the two openings of the middle ear into the 

 inner ear, which are known as the fenestra vestibuli (ovalis) and the 

 fenestra cochleae (rotunda) ; (3) the internal ear with its vestibule, its 

 snail-shell-like cochlea, and the three semicircular canals; the last serve 

 the purpose of equilibrium; (4) the auditory or acoustic nerve, leading 

 from the internal ear to the central nervous system. 



The human visual apparatus (Fig. 248) consists of (1) the eyeballs 

 with their six muscles for eye movement (the superior and inferior recti 

 muscles, the external and internal recti, the superior and inferior oblique 

 muscles) (Fig. 249), (2) the lacrimal apparatus to keep the eye moist 

 and protect it, (3) the conjunctiva or mucous lining of the paired eyelids 

 internally, (4) the eyebrows for protection; (5) the complicated appa- 

 ratus of lens, aqueous humor (in anterior chamber), vitreous body, iris, 

 pupil, cornea, and the sensitive retina, choroid coat, the sclera, etc., (6) 

 the optic nerve, which transmits the stimuli recorded by the retina to the 

 visual centers of the brain where the sensation of sight is really located. 



The human olfactory apparatus consists of a fine network of olfactory 

 nerves spread over the irregular surfaces of the superior nasal conchae 

 and upper nasal septum (Fig. 234). These nerves terminate in olfactory 

 cells, each with six to eight hairlike processes. The latter are affected by 

 small particles of solids or gases in solution. The olfactory nerve carries 

 the impulses to the olfactory center of the brain (Figs. 246 and 247). 



The spinal cord consists of a central canal surrounded by a central 

 core of gray m,atter which is surrounded by white matter. The gray 

 matter in cross section resembles the letter H, the two forward projections 

 being called anterior colum.ns and the two backward projections, the 

 posterior columns. The spinal cord serves as a center for spinal reflexes 



