80 INNEKVATION. [CHAP.XVIII. 



Thus the cochlear muscle is broad at its origin from the groove 

 of bone, and slopes above and below to the thin margin in which it 

 terminates, so that its section is triangular, and it presents three 

 surfaces, one towards the groove of bone, and one to each of the 

 scalae. The surface towards the vestibular scala is much wider than 

 that towards the tympanic scala, and presents, in a band running 

 parallel to and at a short distance from the margin of the mem- 

 branous zone, a series of arched vertical pillars, with intervening 

 recesses, much resembling the arrangement of the musculi pectinati 

 of the heart (fig. 140, c). These lead to and terminate in the outer 

 clear belt of the membranous zone, which forms a kind of tendon to 

 the muscle. This entire arrangement is almost sufficient of itself to 

 determine the muscular nature of the structure. If its fibres were 

 of the striped variety no doubt would remain; but its mass, evi- 

 dently fibrous, is loaded with nuclei, and filled with capillaries, fol- 

 lowing the direction of the fibres, and in almost all respects it 

 has the closest similarity to the ciliary muscle of the eye. The nuclei 

 diminish in number as the fibres end in the tendinous part; and they 

 are made much more evident by the addition of the acetic acid. The 

 action of the muscle must be that of making tense the membranous 

 portion of the lamina spiralis, and so perhaps of adjusting it to the 

 modifications of sound. As the ciliary muscle, though of the un- 

 striped variety, adjusts the transparent media of the eye to distinct 

 vision at different distances under the guidance of the will, so it is 

 not impossible Jthat the cochlear muscle may have a voluntary ad- 

 justing power, though its precise mode of action as a part of an 

 acoustic apparatus may still remain obscure. On the whole, how- 

 ever, we are more disposed to regard this very interesting structure 

 as having a preservative office, as being placed there to defend the 

 cochlear nerves from undue vibrations of sound, in a way analogous 

 to that in which the iris protects the retina from excessive light. 

 These nerves are acted on principally by vibrations brought through 

 the osseous part of the cochlea, and it is probable that the arrange- 

 ment of the scalse is one designed to allow of protective movements 

 of the lamina spiralis by muscular action, under a stimulus reflected 

 from impressions on the auditory nerve. 



The capillaries of the ciliary muscle are derived from vessels 

 meandering over the walls of the scalse before entering it, and 

 those from above and below do not anastomose across the line of 

 attachment of the membranous zone, thus indicating that the con-' 

 tinuation of this zone enters as a plane of tendon into the interior of 

 the muscle, dividing it into two parts, and receiving the fibres in 

 succession. 



