638 TEXT-BOOK OF PHYSIOLOGY. 



dividing several times terminates in a ribbon-like or spiral manner around the 

 intra-fusal muscle fiber. This ending was described by and is known as 

 Rufnni's " annulo-spiral ribbon." The motor nerve also penetrates the 

 capsule and terminates in the polar extremities of the intra-fusal fiber. 

 Sensor end-organs supposed to be connected with the muscle sense are also 

 found in the tendons 'of muscles. 



Afferent Nerves. That muscles are abundantly supplied with afferent 

 nerves has been proved by different methods of investigation. With histo- 

 logic methods Sherrington has traced afferent fibers from the muscle spindles 

 directly into the spinal nerve ganglia. The contractions of muscles from 

 electric stimulation as well as the contractions known as muscle cramp, 

 due to unknown agents, give rise to sensations of pain, a fact which in- 

 dicates the presence in muscles of afferent or sensor nerves. 



Cortical Area.- Pathologic findings have shown that an impairment 

 or a loss of the muscle sense is associated with destructive lesions of perhaps 

 the super- and sub-parietal convolutions (Figs. 252, 253). In a case reported 

 by Starr the removal of a small tumor in the pia mater situated over the 

 junction of the superior and inferior parietal lobules was followed by a loss 

 of the muscle sense and marked ataxia in the right hand for a period of six 

 weeks, after which recovery took place. These symptoms were attributed 

 to injury of the cortex from unavoidable surgical procedures. 



The muscle sensations, as stated in foregoing paragraphs, form the 

 basis of the perception not only of the direction and the duration of a body 

 movement and the resistance experienced, but also of the position and the 

 tension of the muscle groups. The latter fact more especially makes it 

 possible for the mind to direct the muscles and to graduate the energy 

 necessary to the accomplishment of a definite purpose. 



Active Touch. Active touch or the application of the fingers to the 

 surfaces of external objects implies the cooperation of the skin and the muscles. 

 The sensations which are evoked are combinations of contact and muscle 

 sensations. The union of these sensations forms the basis of the perception 

 of hardness, softness, smoothness, and roughness of bodies. 



THE SENSE OF TASTE. 



The physiologic mechanism involved in the sense of taste includes the 

 tongue, the gustatory nerves (the chorda tympani and the glosso-pharyngeal), 

 their cortical connections and nerve-cells in the gray matter of the fourth 

 temporal convolutions. The peripheral excitation of this apparatus gives 

 rise to nerve impulses which transmitted to the brain evoke the sensations of 

 taste. The specific physiologic stimulus is matter, organic and inorganic, 

 in a state of solution. 



The Tongue. The tongue consists of both intrinsic and extrinsic mus- 

 cles, in virtue of which it is susceptible of a change both in shape and in 

 position. The movements of the tongue, though not essential to taste, are 

 made use of in the finer discrimination of tastes. 



The tongue is covered over by mucous membrane continuous with that 

 lining the oral cavity. The dorsum of the tongue presents a series of papillae 

 richly supplied with blood-vessels and nerves. Of these there are three 

 varieties, the filiform, the fungiform, and the circumvallate (Fig. 300). 



