AUDITOEY OSSICLES. 841 



the presence of a synovial cavity and regard the articulation as a syndesmosis, the 

 articular surfaces being held together by fibrous tissue. 



Ligamenta Ossiculornm Auditus. The malleus is attached to the walls of the 

 tympanic cavity by three ligaments (Fig. 715), viz. : anterior, superior, and lateral. 

 The anterior ligament consists of two portions : (a) the band of Meckel, which is 

 attached to the base of the processus anterior, and passes forwards, through the petro- 

 tympanic fissure, to reach the spine of the sphenoid ; it represents the remnant 

 of a portion of Meckel's cartilage, and was formerly described as the laxator tympani 

 muscle; (&) a firm bundle of fibres, the anterior ligament of Helmholtz, which 

 extends from the spina tympanica anterior at the anterior boundary of the notch 

 of Kivinus to the anterior surface of the malleus, above the base of the processus 

 anterior. The superior ligament stretches, almost vertically, from the head of the 

 malleus to the roof of the epitympanic recess. The lateral ligament is short and 

 fan-shaped ; its fibres converge from the posterior half of the notch of Kivinus to 

 the crista mallei. The posterior part of this ligament is strong and constitutes 

 the posterior ligament of Helmholtz ; it forms, together with the anterior ligament 

 of the malleus, the axis around which the malleus rotates, and the two constitute 

 what Helmholtz termed the " axis-ligament " of the malleus. 



The posterior extremity of the crus breve of the incus is tipped with cartilage 

 and fixed by means of a ligament to the fossa incudis (Fig. 715). Some observers 

 describe this as a diarthrodial joint. The vestibular surface and the circum- 

 ference of the base of the stapes are covered with hyaline cartilage, and a similar 

 layer lines the opening of the fenestra vestibuli; that encircling the base of the 

 stapes is joined to that lining the fenestra by a dense ring of elastic fibres, 

 named the ligamentum annulare baseos stapedis. The posterior fibres of this 

 ligament are thicker and shorter than the anterior, and thus during the movements 

 of the stapes, the anterior end of its base is free to make greater excursions than 

 the posterior. 



Development of the Auditory Ossicles. It is generally maintained that the 

 malleus and incus are developed from the upper end of Meckel's cartilage, and that the 

 stapes arises from the mesoderm in the region of the fenestra vestibuli, where it is developed 

 around a small artery, the stapedial artery, which atrophies in man, but persists in many 

 mammals. On the other hand, Gadow (Phil. Trans., London, vol. clxxix.) says "the whole 

 system of the one to four elements of the middle ear, which have all the same function, 

 is to be looked upon as one organ, of one common origin, viz., a modification of the hyo- 

 mandibular, the proximal paramere of the second visceral arch." Ossification commences 

 in all three bones about the third month of foetal life. The malleus is ossified from two 

 centres, one for the head and manubrium, and one for the processus anterior ; the incus 

 from two centres, one for the body including the crura, and a second for the processus 

 lenticularis ; the stapes from one centre which appears in the base. 



Muscles of the Tympanic Cavity. These are two in number, viz., m. tensor 

 tympani and m. stapedius. 



The m. tensor tympani is the larger, and takes origin from the roof of the carti- 

 laginous part of the auditory tube, from the adjacent part of the great wing of the 

 sphenoid, and from the bony canal in which the muscle lies. The muscle ends in a 

 tendon which bends laterally, nearly at a right angle to the belly of the muscle, 

 round the pulley-like posterior extremity of the septum canalis musculotubarii. 

 Passing across the tympanic cavity this tendon is inserted into the medial edge 

 and anterior surface of the manubrium mallei, near its upper end. When the 

 muscle contracts it draws the manubrium of the malleus towards the tympanic cavity, 

 and so renders tense the membrana tympani ; it probably also slightly rotates the 

 malleus around its long axis. It receives its nerve from the motor division of the 

 trigeminal nerve, through the otic ganglion. 



The m. stapedius arises within the eminentia pyramidalis, and from the canal 

 which prolongs the hollow of the pyramidal eminence downwards. Its tendon 

 emerges from the apex of the eminence and is inserted into the posterior surface 

 of the neck of the stapes. On contraction it draws back the head of the stapes, 

 and so tilts the anterior end of the base towards the tympanic cavity and the 



