OF THE MAMMALIAN OSSICULA AUDITUS. 479 



eaters just named the flattening is greater and the head itself larger. In the narrow 

 curved neck the same animals resemble the Kangaroos rather than Man and the higher 

 Monkeys, and differ in having a distinct neck from the Cebidse. But as to the lamina, 

 which is absent in Homo and the Quadrumana and Lemures, it is well developed in the 

 small-headed malleus of a Carnivore or Ruminant, but ill developed, though existent, in 

 Macropus. A similar degree of partial development has already been noted in some 

 Edentata, as in Choloepus or Myrmecophaga ; and it is to be remembered that the same 

 condition may be said to exist in Priodon, whilst Tolypeutes possesses a lamina as wide 

 as in many Carnivora ; so that the latter genus differs from Priodon in one way, as 

 Dasypus does in a much higher direction, the head of the malleus being almost 

 anthropoid in development. On the other hand the lamina is again suppressed in Manis, 

 and the articular surface is singularly like that of Homo, though the head is ill deve- 

 loped, and the stapes of a lower type than in Macropus, much lower than in Dasypus. 



Erom the above facts, it appears to me to be justifiable to consider that the narrow- 

 necked and narrow-laminated type of malleus, as seen in Macropus, is the lowest form, 

 which has become developed, in higher mammals, into two higher forms : — one where 

 the lamina is more developed, as in the Carnivora ; the other where the neck is stouter 

 or even merged into the head, as in Homo and the Quadrumana. The latter form 

 must be considered the highest, not only because it exists in Man, but also because 

 the former, or laminated type, most resembles the Kangaroo's malleus in the form 

 of the head, and in the neck being equally long, narrow, and slightly curved ; indeed, 

 in the very Orders where the laminated type prevails, the occasional partial or complete 

 suppression of the characteristic lamina is often associated with an increased develop- 

 ment of the head, and a greater stoutness or shortness of the neck, as I have already 

 observed in Herpestes and Suricata. 



On the other hand, a form of malleus exists in other Monodelphia where not only are 

 the head, neck, and even the manubrium strikingly like the same in Macropus, and the 

 lamina of like small development, but the latter is prolonged upon a well-developed pro- 

 cessus gracilis in a similar manner. This is the case in Rhinoceros and Priodon. 



Hence not only is the Macropus type of malleus the lowest of the three, but the lami- 

 nated type is clearly the second or the intermediate form, the large-headed and thick- 

 necked form being, therefore, unquestionably the highest ; indeed it is almost as much 

 above the laminated as it is above the Macropoid variety. These observations suggest 

 an easy test of the grade of any mammal when judged by its malleus ; and, as a rule, 

 the other ossicula agree with it. 



In a young Halmaturus, measuring two inches without the tail, I have found the 

 malleus of similar form ; but the head is much larger in proportion to the body than in 

 Macropus * ; the lamina is the same in character and similarly prolonged on the pro- 

 cessus gracilis. 



Supposing, then, that both head and lamina, as existent in the young Halmaturus, 

 remain in a comparatively arrested state of development, the adult must necessarily 



* The same, it is worth recording, is the case in the malleus of the adult Phalanger (PJialangista). 



3s2 



