IX] THE ORGANS OF SPECIAL SENSE 111 



raj)idly. These vibrations are communicated to the bony ossicles, 

 which undergo varied movements. The stapes, which as we have 

 alreadj'^ seen, is attached to the fenestra ovalis, causes this mem- 

 brane to vibrate and so sets up a series of vibratory waves in the 

 Ijerilymph which fills the scala vestibuli. These waves travel up 

 the cochlea, pass through the helicotrema, travel down the scala 

 tympani and end against the fenestra rotimda which in turn is 

 set in vibration. During their passage through the cochlea these 

 vibration waves impinge on the membranes enclosing the canal 

 of the cochlea setting up a sympathetic series of vibrations in the 

 endolymph of the canal of the cochlea and so act on the delicate 

 nerve endings in the organ of Corti. The stimuli thus received 

 are conveyed to the brain and give rise to the sensation of hearmg. 

 The Sense of Taste. The sense of taste is associated with the 

 l^resence of certain well defined groups of cells, called gustatory 

 cells, which are found in the characteristic papillae of the mucous 

 membrane of the tongue and are restricted to well-defined areas. 

 According to their shape, these papillae or projections are called 

 filiform, fungiform and circum vallate papillae, and the fungiform 

 and circumvallate papillae are specially associated with the sense 

 of taste. The gustatory cells are found in bud-Hke groups and are 

 called taste buds. In the ox, the fungiform papillae are numerous 

 and distinct and are found scattered over the dorsum and edges 

 of the free part of the tongue. The circumvallate papillae number 

 8 to 17 on each side and each side forming a narrow group at the 

 edge of the base of the tongue. In the horse the fungiform j^apillae 

 are large and easily seen and occur principally on the lateral j)art 

 of the tongue. The circumvallate papillae are two or three in 

 number, the two constant ones being j in. or more in- diameter and 

 are found on the upper surface of the base of the tongue, one on 

 each side of the middle line about an inch apart. Foliate or leaf- 

 like j^ajjillae are also present on the anterior pillars of the soft 

 palate and contain taste buds. 



Each gustator}' cell is long and very thin, has a large nucleus 

 at its middle point, and ends in a delicate process which projects 

 like a stiff hair through the open mouth of the taste bud. The 

 papillae are supplied with branches from two nerves, the glosso- 

 pharyngeal nerve, and the gustatory nerve which is a branch of 

 the 5th cranial nerve. There is evidence for the belief that different 

 taste sensations are supplied by these two nerves. In the case of 



