222 



MAMMALIAN ANATOMY 



in and out of the fenestra ovalis. In this way the vibrations of sound 

 are transmitted from the exterior to the fluid filling the internal ear 

 and are appreciated by the end filaments of the auditory nerve. 



The Malleus 1 is the largest of the three ossicles, and measures 

 about eight millimetres in length and three millimetres in width. 

 It is composed of an upper broad portion (Fig. 152), and a lower 

 slender portion, called the handle or manubrium, which is longer 

 than the upper portion and is bent forward from it at an angle of 

 about one hundred degrees. 



FIG. 152. 



With Incus.- 



Neck.--- 

 Process for TENSOR ' 



TYMPANI. 



Handle. 



FIG. 153. 



Head.--- 



Head. 



Lamina. 

 Long Process. 



Lateral Facet. - 



Neck.. . 



Short Process 



-\--3fedial Facet. 



Process for 



TENSOR TYMPANI. 



LEFT MALLEUS. MEDIAL ASPECT. 

 (Enlarged Five Times.) 



Handle:- 



LEFT MALLEUS. POSTERIOR ASPECT. 

 (Enlarged Five Times. ) 



FIG. 154. 



Head...- 



Lam in ft. - 

 Long Process.. 



The upper portion is surmounted by an ovoid head, which bears on 

 its posterior aspect (Fig. 153) a deep articular cavity for the head of 

 the incus. This cavity encroaches slightly upon the inner aspect of 

 the bone ; it is divided into two facets by a groove which begins at 



the inner lower border and ends in a 

 circular depression before reaching the 

 upper outer border. The facets slope 

 toward the groove, and each is crossed 

 by a convex ridge, thus producing four 

 articulating surfaces. The upper surfaces 

 of the outer and inner facets together form 

 an almost circular fossa ; the lower surface 

 of the inner facet is flat or gently concave 

 in both directions ; the lower surface of the 

 outer facet is convex in both directions. 

 The head is joined to the handle by a long slender neck (Fig. 

 154), which is cylindrical and describes a sinuous curve outward, in-% 



1 A hammer. 



Neck. 



Short Process. 



- Handle. 



LEFT MALLEUS. LATERAL ASPECT. 

 (Enlarged Five Times.) 



