THE PROPRIO-CEPriVE MECHANISM 



proprio -ccptivo mechanism of the body he is aware of the position of 

 the razor in his hand, and is able to adjust the blade so as to shavo 

 without, at any rate, badly cutting himself. In this, of course, he i j 

 aided by cutaneous tactile sensation, but this, as wo shall see later, 

 is not the factor controlling the main movements. 



The Proprio-ceptive Mechanism of the Head The Labyrinthine 

 Sensations play an important part in the equilibration of the 

 body. The receptor mechanism for these is, as the name signifies, 

 contained within the bony labyrinth of the middle ear, the utricle, 

 and the three membranous semicircular canals. The utricle connects 

 with the saccule, and lies in the vestibule of the internal ear. From 



FIG. 382. PHOTOGRAPH SECTION THROUGH CRISTA OF THE AMPULLA OF THE 

 GUINEA-PIG. (H. Pringle, from " Quain's Anatomy.") 



In lowest part of section nerve-fibres are seen passing through the bone to the loose 

 tissue below the crista. The epithelial cells of the crista are pear-shaped sur- 

 mounted by hairlets projecting into a mueinous material. 



it also arise the three membranous semicircular canals which lie 

 within the bony semicircular canals, and connect with the utricle by 

 five openings. The bony semicircular canals arise from the posterior 

 and superior aspect of the vestibule, each canal having at one end a 

 swelling, or ampulla. They are arranged at right angles to one 

 another, two in a vertical and one in the horizontal plane. The 

 latter is known as the external canal. It lies horizontally, with its 

 curves outwards and the ampulla in front. 



Of the vertical canals, one is termed the anterior, or superior, the 

 other the posterior. The horizontal canals occupy approximately 

 the same plane. The superior canal lies in a plane inclined at an 



