102 



Mr. Alban H. G. Dor an on the 



[June 15, 



Anatomy of the Internal Auditory Apparatus of the Mammalia *, but 

 the subject of the ossicula themselves has not been considered in that 

 able treatise quite fuUy and precisely enough for the present purpose. 



All the Mammalia are known to possess three of these small bones, 

 named respectively the malleus, the incus, and the stapes ; the two 

 former are occasionally fused. Their form and characters in our own 

 species may be regarded as fairly typical, so that it is advisable to 

 commence the subject by considering the ossicula of Homo. 



Speaking from the stand-point of comparative anatomy, we may 

 describe the malleus of man as having a well-developed head somewhat 

 compressed antero-posteriorly and expanded laterally. It rises con- 

 siderably above its articular region, and bulges markedly in an outward 

 direction. The articular surface lies on the posterior aspect of the head 

 very obliquely, so that its external extremity lies much higher than the 

 internal. It is generally spoken of by human anatomists as forming one 

 single saddle-shaped facet ; but on comparing it with the same surface in 

 the malleus of most of the lower mammalia, say in a cat or a pig, it vrill 

 be seen that it is in reality made up of two facets, much less distinct 

 than in those animals, but more marked than in many monkeys. A 

 very faint groove divides them, and runs in the very oblique long axis 

 of the whole surface. The more internal and upper facet above this 

 groove represents that which is almost completely superior in the lower 

 animals, the more external, below the groove, corresponding to their 

 lower facet. Both rise into a high vertical convexity about the middle 

 of the surface, where the latter is a little contracted ; their planes slope 

 towards the groove, so that the articular surface appears concave, 

 especially when viewed sideways. 



The neck of the human malleus is constricted and shorter than in 

 most of the Mammalia, though longer than in most of the Primates. 

 On its extero-superior aspect is a sharp sigmoid ridge, beginning near 

 the anterior border of the articular surface, and losing itself on the root 

 of the manubrium. This ridge is of the same form, and probably repre- 

 sents the sharply curved entire neck of the malleus of most Carnivora 

 and Euminants and many other Mammalia, where a bony lamella 

 extends from that portion as far as the processus gracilis. A very faint 

 trace of that " lamina," as it may briefly be called, may be seen extend- 

 ing, in a fully developed foetal human maUeus, from the neck to the root 

 of the processus gracilis; but it seems reasonable to infer that the stout, 

 compact portion of the neck in front of the sigmoid ridge represents in 

 a more solid form the lamina referred to. Close to the root of the 

 manubrium, and on the inner side, a very faint eminence, to which the 

 tensor tympani is attached, represents the processus muscularis of some 

 other mammals. The well-known processus gracihs of the malleus of 

 Homo is kno^n to be to a great extent absorbed in the process of extra- 



* Vergleichend-anatomische Untersuchungen iiber das innere Gehororgan des 

 Meuschen und der Saugethiere. Prague, 1845. 



