224 



MAMMALIAN ANATOMY 



composed of two facets (Fig. 157), but the directions of their surfaces 

 are, of course, reversed. 



FIG. 156. 



FIG. 157. 



f\..- Superior Process. 



With Malleus.- yCTN J ^^ > ' Superior Process. 



\5- Inferior Process. 



LEFT INCUS. LATERAL ASPECT. 

 (Enlarged Five Times.) 



Medial Facet .-gS^'git- Lateral Facet. 



Lenticular Process., 

 with Stapes. 



LEFT INCUS. ANTERIOR ASPECT. 

 (Enlarged Five Times.) 



Of the two processes of the incus, the superior process is the 

 shorter and more conical. It is directed almost horizontally backward 



in the fossa formed between the squa- 

 mous and the bridge (see p. 196), and 

 its end is attached to the squamous by 



FIG. 158. 



Q With Malleus. 



Superior Process. - 



\-h Inferior Process. 



Lenticular Process,,..^/ 



with Stapes. 



LEFT INCUS. MEDIAL ASPECT. 

 (Enlarged Five Times.) 



a ligament. 



FIG. 159. 



With Incus. 



The inferior process (Fig. 158) is 

 longer, and projects downward, back- 

 ward, and outward ; its end is bent 



sharply inward and upward and terminates in a small orbicular or 

 lenticular tubercle which articulates with the stapes. In early life 

 this tubercle is a separate element in the chain of ear-ossicles. 



The Stapes x (Fig. 159) is the smallest of the three ossicles : 

 its greatest diameter measures but two millimetres. It has the exact 

 shape of a stirrup, and consists of a small 

 disk- like head, resting on a larger body, 

 which becomes gradually flattened from 

 above downward until its cross-section 

 becomes oval. On its posterior aspect 

 is a small tubercle for the attachment 

 of the stapedius muscle. The body 

 splits into two crura 2 which surround an 



oval opening, filled in the recent state by a membrane attached in a 

 groove. The posterior crus is shorter and stouter than the anterior 

 crus. The base of the stapes is a thin oval plate, the lower edge of 

 which is straighter than the upper edge. The outer side is joined at 

 each end to the inner end of one of the crura in such manner as to 



Process for STAPEDIUS - 



Posterior Crus.--- 

 Oroovefor Membrane. - 



He ml. 

 -Body. 



-Anterior Crus. 

 r 'Opening . 



Base, fills Fcnestra Ovalis. 



LEFT STAPES. INFERIOR ASPECT. 

 (Enlarged Five Times.) 



1 A stirrup. 



Thighs; singular cnts, a thigh. 



