THE EAR 



1543 



Short Process 



Long Process 



Fig 



. J^nticular Process fot 

 Head of Stapes 



The Ixccs. 



647. 

 ( Postero-intemal View). 



t^^npani, with which it is connected by the annulus fibrosus. It 

 is also connected with the extremities of the notch of Rivini by those 

 bands of the annulus fibrosus which are known as the anterior and 

 posterior malleolar ligaments. 



The incus has been so named from its resemblance to an anvil. 

 It consists of a body and two processes — short and long. The body 

 is thick, somewhat four-sided, and 

 laterally compressed. Anteriorly it 

 presents a saddle-shaped articular sur- 

 face for the head of the malleus, with 

 which it forms a synovial joint. The 

 short process is directed backwards, is 

 tipped with cartilage, and articulates 

 with the fossa incudis on the posterior 

 wall of the tympanum. The long pro- 

 cess is directed downwards and in- 

 wards, behind and parallel to the 

 handle of the malleus. Its lower ex- 

 tremity is bent inwards, and becomes 



narrowed into a neck, upon which is placed a disc-like knob of 

 bone, called the processus lenticularis seu orbicularis, which is 

 covered by cartilage for articulation with the head of the stapes. 

 In early life, and up to the sixth month of intra-uterine life, this 

 process forms a separate ossicle, called the os orhicidare. 



The stapes is so named from its resemblance to a stirrup. It 

 consists of a head, neck, two crura, and a 

 ^ foot-piece or base. The head is directed 



outwards, is concave and covered by 

 cartilage, and articulates with the pro- 

 cessus lenticularis of the incus. The 

 neck is the constricted part which lies 

 immediately internal to the head. Pos- 

 teriorly it gives insertion to the stapedius 

 muscle. The crura are anterior and pos- 

 terior respectively, and spring from the 

 neck. They diverge as they pass in- 

 wards, and are attached to the foot- 

 piece near its extremities. The anterior 

 cms is straighter and shorter than the 

 posterior. The foot-piece or base is some- 

 what oval, is directed inwards, and 

 occupies the fenestra ovalis, which it 

 almost completely fills; its circumference 

 is covered by cartilage, being attached to the margins of the 

 fenestra by annular ligamentous fibres. The arch formed by the 

 crura and foot-piece is occupied by a delicate membrane, which is 

 attached to a slight groove on the inner aspect of the arch. 



Development of the Tympanic Ossicles. — The malleus and incas are usually 

 regarded as being developed from the proximal end of Meckel's cartilage. 



Head 



Stapes.- 



FiG. 648. — (i) The Stapes, 

 AND (2) Tympanic Ossi- 

 cles IN Position. 



