BONES OF TliE.EAR. ORBICULARE. STAPES. 461 



angle with its body, the salient side of the angle presenting 

 outwards ; the space from this angle to the termination of the 

 manubrium, or in oilier words the whole manubrium is con- 

 nected with the membrana tympani. 



The Incus resembles a molar tooth, with two roots, widely 

 separated from each other. On the body is a depression which 

 is connected with the head of the malleus. One of the roots 

 or crura is much longer than the other. 



The Os Orbiculare is equal in size to a small grain of sand. 

 It is connected to the extremity of the long crus of the incus, 

 and to the upper part of the stapes. 



The Stapes has a strong resemblance to the common stirrup. 

 The upper part is called its head, the lower part its base, and 

 the two lateral portions its crura. One of the crura is longer 

 than the other. A groove is also observed on the inner side of 

 its crura, when they are examined with a microscope. The 

 base is applied to the Foramen Ovale. 



The situation of these bones is such that the head of the 

 malleus and the body of the incus are in the upper and anterior 

 part of the cavity of the tympanum, which extends above the 

 membrana tympani. The malleus is the most anterior of 

 the two bones : its manubrium projects downwards, and is 

 included between the internal lamen of the membrana tym- 

 pani and the membrane itself. Its long process extends hori- 

 zontally inwards and forwards, into the fissure of the glenoid 

 cavity. 



The incus is so placed that the depression on its body re- 

 ceives the head of the malleus. The shortest leg projects 

 backwards horizontally, and is attached by a ligament to a 

 point in the opening into the mastoid cells. While the long 

 leg projects downwards like the handle of the malleus, but 

 behind it, and at a small distance inwards from the membrana 

 tympani. 



The situation of the stapes is almost at right angles with the 

 long leg of the incus, projecting inwards. Between the head 

 of the stapes and the long leg of the incus, the os orbiculare 

 intervenes. 



39* 



