300 ANIMAL MECHANISM. 



Two of these canals, as they wind towards the side of 

 the vestibule, coalesce and when they perforate the 

 wall, have only one orifice in common. The third 

 enters alone, and this explains the two holes seen on one 

 side of the vestibule ; on the opposite side are three 

 holes, being the orifices of the same three canals, open- 

 ing singly. When the semi-circular canals are closely 

 examined, they are observed to be larger at one ex- 

 tremity, near the walls of the vestibule, than at the other, 

 the bulbs or bulges are termed ampullulcB or bottle 

 shaped. A crook-neck squash is an exact, though 

 greatly magnified representation of any one of the semi- 

 circular canals. The diameter of the circle of which 

 they are a little more than two thirds of a segment, varies 

 but little from one quarter of an inch in man ; and the 

 calibre of the canals themselves will scarcely admit the 

 introduction of a fine bristle. A probable reason for the 

 swelling out of the ampullulse will be given when dis- 

 coursing particularly on the nerve. 

 FIG. 8. 



Explanation of Figure 8. 



In this enlarged diagram of the labyrinth which is laid open, 

 the soft parts are seen. Some of my readers, particularly young 



