THE SENSE OF POSITION. STATIC SENSE 



783 



latter it tapers into a narrow duct, measuring 1 mm. 

 in length and 0.5 mm. in height. It finally connects 

 with the central canal of the cochlea a short distance 

 above its expanded lower extremity. The other 

 pole of the saccule communicates with the utricle 

 by means of the ductus endolymphaticus. The 

 utricle is irregular in shape and measures 6-7 mm. 

 in length and 5 mm. in breadth. It gives origin to 

 the semicircular canals. Of particular importance 

 to us at this time is the so-called recessus utriculi, 

 a blind forward projection from the main cavity 

 which contains the macula acustica. This area is 

 formed by auditory epithelium which is beset with 

 hair-like processes carrying otolithic crystals, and is 

 innervated by fibers from the auditory nerve. A 

 similar patch of sensory epithelium is contained in the 

 saccule. 



Three views have been held regarding the func- 

 tion of the macula utriculi and macula sacculi, 

 namely (a) that they are the recipients of the sound 

 waves, (h) that they mediate irregular vibrations or 

 noises, and (c) that they serve the purpose of stato- 

 lithic organs. The first contention may be dis- 

 carded, because it has now been thoroughly estab- 

 lished that the cochlea is fully capable of taking care 

 of this function. The second view is based merely 

 upon assumptions and need not be discussed further. ' 

 By exclusion, therefore, this discussion may be re- 

 stricted to the view of Brener,^ which holds that 

 these structures inform us regarding the position of 

 the head when at rest or when the entire body is en- 

 gaged in making progressive movements in one direc- 

 tion or another. It is conceived that the otolithic, 

 or rather, statolithic crystals evoke stimulations by 

 means of their weight resting upon the neighboring 

 hair-like processes. This weight, of course, is not 

 objective, but is lessened somewhat by the fact that 

 it is exerted in a medium of endolymph. At any 

 time when the head is tilted, their lines of gravity 



/ 



\ 



'rt 



7 



Fig. 396. — Nerve-endings upon the Intrafusal Muscle-fibebs of a Muscle-spindle 

 OF THE Rabbit. Moderately Magnified. Methylene-blue Preparation. (Dogiel.) 



a, Large medullated fiber coming off from 'spindle' nerve and passing to end in an 

 annulo-spiral termination on and between the intrafusal fibers; b, fine medullated 

 fiber coming off from the same stem and dividing. Its branches, c, pass towards the 

 ends of the muscle-fibers and terminate in a number of small localized arborizations, like 

 end-plates. 



1 Pfliiger's Archiv, Ixviii, 1897, 596. 



