AUDITORY OSSICLES. 



839 



inwards, the malleus, incus, and stapes. The first is attached to the medial 

 surface of the mernbrana timpani ; the last is fixed within the circumference of 

 the fenestra vestibuli. 



The malleus (Fig. 714, B, D), the largest of the three ossicles, has a length of 

 8 to 9 mm., and consists of a head, a neck, a manubrium, and two processes, viz. : 



FIG. 714. AUDITORY OSSICLES OF LEFT EAR (enlarged about three times). 



A, Incus, seen from the front ; B, Malleus, viewed from behind ; C, Incus, and D, Malleus, seen from medial 



aspect ; E, Stapes. 



1. Body of incus, with articular 



surface for head of malleus. 



2. Crus longum. 



3. Processus lenticularis. 



4. Articular surface for incus. 



5. Head of Malleus. 



6. Neck of Malleus. 



7. Processus lateralis. 



8. Manubrium. 



9. Body of incus. 



10. Crus breve. 



11. Crus longum. 



12. Processus anterior. 



13. Head of malleus. 



14. Facet for incus. 



15. Manubrium. 



16. Head of stapes. 



17. Neck. 



18. Crus anterius. 



19. Crus posterius. 



(a) processus anterior, (5) processus lateralis. The head and neck are situated in 

 the epityrnpanic recess ; the processus lateralis and manubrium are fixed to the 

 medial surface of the membrana tympani; while the processus anterior is directed for- 

 wards, towards the petro-tympanic fissure, to which, in the adult, it is connected by 

 ligamentous fibres. The head, somewhat rounded, is smooth and convex above and 

 in front, and presents, on its posterior surface, a facet for articulation with the body 



Recessus epitympanicus 

 Body of incus 



Crus breve of incus 

 Ligament of incus 



Chorda tympani nerve 



Eminentia pyramid- 



alis, with tendon of 



in. stapedius issuing 



from it 



Base of stapes 



Superior ligament of malleus 

 Head of malleus 



Anterior ligament of malleus 

 Manubrium mallei 



Fio. 715. LEFT MEMBRANA TYMPANI AND CHAIN OF AUDITORY OSSICLES (seen from the medial aspect), x 3. 



of the incus. This facet is directed obliquely downwards and medialwards, and is 

 more or less elliptical in form. It is constricted near the middle so as to resemble, 

 somewhat, the figure 8 ; an oblique ridge, corresponding with the constriction, 

 divides the facet into two parts an upper and larger, directed backwards, and a 

 lower and lesser, directed medialwards. Opposite the lower part of the constriction 

 the inferior edge of the facet is very prominent, and is continued upwards into the 

 oblique ridge just referred to ; it forms a tooth-like process, the spur or cog-tooth of 



