THE MIDDLE EAR, DRUM, OR TYMPANUM 



1133 



consists of two strata an external, of radiating fibres (stratum radiatum), which diverge from 

 the handle of the malleus, and an internal, of circular fibres (stratum rirculare), which are plenti- 

 ful around the circumference, but sparse and scattered near the centre of the membrane. 

 Branched or dendritic fibres, as pointed out by Griiber, are also present, especially in the pos- 

 terior half of the membrane. 



The arteries are derived from the deep auricular branch of the internal maxillary, which 

 ramifies beneath the cuticular layer and from the stylomastoid branch of the posterior auricular 

 and tympanic branch of the internal maxillary, which are distributed on the mucous surface. 

 The arteries of the cutaneous set anastomose with the arteries of the mucous set by minute 

 branches which penetrate the drum membrane near its margin. The superficial veins open 

 into the external jugular; those on the mucous surface drain partly into the lateral sinus and 

 veins of the dura and partly into a plexus on the Eustachian tube. The outer surface of the 

 drum membrane receives its nerve supply from the auriculotemporal branch of the inferior 

 maxillary and the auricular branch of the vagus. The inner surface is supplied by the tym- 

 panic branch of the glossopharyngeal. 



There are two sets of lymphatics, the cutaneous and mucous, which freely communicate. The 

 spaces between the dendritic fibres of Griiber are lymph spaces (Kessel). 



The Ossicles of the Tympanum (ossicula auditus) (Fig. 840). The tym- 

 panum contains in its upper part a chain of movable bones, three in number, 

 the malleus, incus, and stapes. The first is attached to the membrana tvmpani. 

 the last to the fenestra ovalis. the incus being 

 placed between the two, and connected to 

 both by delicate articulations. 



The Malleus (Fig. 841), so named from its 

 fancied resemblance to a hammer, is placed 

 farthest in front and outward. It consists 

 of a head, neck, and three processes the 

 handle, or manubrium, the processus gracilis, and 

 the processus brevis. 



The head (capitulum mallei) is the large 

 upper extremity of the bone, and is situated 

 in the epitympanic recess (Fig. 838). It is 

 oval in shape, and articulates posteriorly with 

 the incus, being free in the rest of its extent. 

 The facet for articulation with the incus is 

 covered by cartilage; it is constricted near 

 the middle, and is divided by a ridge into an 

 upper, greater, and a lower, lesser part; which 

 form nearly a right angle with each other. 

 Opposite the constriction the lower margin of 

 the facet projects in the form of a process, 

 the cog tooth, or spur of the malleus. On the 

 back of the head below the spur is a crest 

 (crista mallei), to which the posterior ligament 

 of the malleus is attached. 



The neck (collum mallei) is the narrow contracted part just beneath the head: 

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

 chorda tympani nerve'crosses the inner surface (Fig. 838). 



The handle (manubrium mallei) is a vertical process of bone, which is connected 

 by its outer margin with the fibrous layer of the membrana tympani, its entire 

 length being fastened to the fibrous layer of the drum membrane by its own peri- 

 osteum and by a layer of cartilage (Figs. 838 and 840). It is directed downward, 

 inward, and backward; it decreases in size toward its extremity, where it is curved 

 slightly forward, and is flattened from within outward. The handle forms a 

 variable angle with the head of the hammer. It averages about 130 degrees, 

 but is always greater in the right ear than in the left. It forms an angle with the 



FIG. 840. Chain of ossicles and their liga- 

 ments, seen from the front in a vertical, 

 transverse section of the tympanum. (Testut.) 



