OSSICLES OF THE TYMPANUM. 635 



attached to the membrana tyrnpani, the latter to the fenestra ovalis, the incus 

 being placed between the two, to both of which it is connected by delicate 

 articulations. 



The Malleus, so named from its fancied resemblance to a hammer, consists of a 

 head, neck, handle or manubrium, and two processes, viz., the processus gracilis 

 and the processus brevis. 



The head is the large upper extremity of the bone ; it is oval in shape, and 

 articulates posteriorly with the incus, being free in the rest of its extent. 



The neck is the narrow contracted part just beneath the head ; and below this 

 is a prominence, to which the various processes are attached. 



The manubrium is a vertical portion of bone, which is connected by its outer 

 margin with the membrana tympani. It decreases in size towards its extremity, 

 where it is curved slightly forwards, and flattened from within outwards. 



The processus gracilis is a long and very delicate process, which passes from 

 the eminence below the neck forwards and outwards to the Glaserian fissure, to 

 which it is connected by bone and ligamentous fibres. It gives attachment to the 

 Laxator tympani. 



The processus brevis is a slight conical projection, which springs from the root 

 of the manubrium, and lies in contact with the membrana tympani. Its summit 

 gives attachment to the Tensor tympani. 



The Incus has received its name from its resemblance to an anvil, but it does 

 not look unlike a bicuspid tooth, with two 

 roots, which differ in length, and are widely 

 separated from each other. It consists of a 

 body and two processes. 



The body is somewhat quadrilateral, but 

 compressed laterally. Its summit is deeply 

 concave, and articulates with the malleus ; in 

 the fresh state, it is covered with cartilage 

 and lined with synovial membrane. 



The two processes diverge from one 

 another nearly at right angles. 



The short process, somewhat conical in 

 shape, projects nearly horizontally back- 

 wards, and is attached to the margin of the 

 opening leading into the mastoid cells by 

 ligamentous fibres. 



The long process, longer and more slender than the preceding, descends nearly 

 vertically behind the handle of the malleus, and, bending inwards, terminates in a 

 rounded globular projection, the os orbiculare, tipped with cartilage, and articu- 

 lating with the head of the stapes. In the foetus the os orbiculare exists as a 

 separate bone, but becomes united to the long process of the incus in the adult. 



The Stapes, so called from its close resemblance to a stirrup, consists of a head, 

 neck, two branches, and a base. 



The head presents a depression, tipped with cartilage, which articulates with 

 the os orbiculare. 



The neck, the constricted part of the bone below the head, receives the insertion 

 of the Stapedius muscle. 



The two branches or crura diverge from the neck, and are connected at their 

 extremities by a flattened, oval-shaped plate (the base), which forms the foot of 

 the stirrup, and is fixed to the margin of the fenestra ovalis by ligamentous fibres. 



Ligaments of the Ossicula. These small bones are connected with each other, 

 and with the tympanum, by ligaments, and moved by small muscles. The articular 

 surfaces of the malleus and incus, the orbicular process of the incus and the head 

 of the stapes, are covered with cartilage, connected together by delicate capsular 

 ligaments, and lined by synovial membrane. The ligaments connecting the ossicula 

 with the walls of the tympanum are three in number, one for each bone. 



