OF THE MAMMALIAN OSSICULA AUDITUS. 373 



conspicuous changes during growth in some genera, whilst in others no such alterations 

 take place. Hence the advisability of procuring young as well as adult ossicula, before 

 coming to conclusions with regard to peculiarities in any group,, is manifest. 



Between the head and the manubrium is the short, constricted " neck." This is 

 rather flattened laterally, so as to be narrower in its vertical than in its horizontal measure- 

 ment. On its external aspect is a sharp sigmoid ridge *, convex forwards at first, where 

 it is near the anterior border of the articular surface, then concave forwards, where its 

 anterior end loses itself on the root of the manubrium (PI. LVIII. fig. 30). I call 

 particular attention to this ridge, as it is almost constant in those animals where the 

 malleus has a distinct neck, and is very plain in the mallei of the fissiped Carnivora and 

 most Ungulates, appearing as the sharply curved compact neck itself, the remainder 

 being a thin lamella of bone joining the processus gracilis. In the Common Badger 

 (Meles taxus) it will be seen to curve so sharply as to form a distinct projection. 



Observe that this sigmoid portion — evidently the essential part of the neck, if we give 

 that name to the bony isthmus which seems made to unite the head to the manubrium — 

 runs away from the processus gracilis, but is lost on the base of the manubrium. This is 

 easily accounted for when we remember that the neck is originally developed from the 

 incurved dorsal end of the mandibular arch, the apex of which forms the manubrium itself, 

 Professor Parker has recently shown f. 



On the anterior aspect of the neck, close to the root of the manubrium, is the root or 

 place of origin of the processus gracilis. Now, after examining numerous mallei from 

 human foetal and adult skulls, I have hardly ever found a trace of the wide lamina of 

 thin bone filling up the angle that process forms with the neck as in the fissiped 

 Carnivora. But as I believe the sigmoid posterior part of the neck in Homo to 

 represent the similar curved isthmus which constitutes the whole neck (independently 

 of the lamina) in these animals, I consider it correct to say that the stout compact 

 portion of the " neck " of human anatomists in front of that sigmoid ridge is really 

 the same ossification as the upper part of the lamina, when such exists — the lower 

 being absent in any form, whether compact or papery. In good specimens from a 

 foetus at full term, it will be seen that a little fringe of friable bone extends as far 

 upwards as the front of the head, which latter, in these cases, sends forward a slight 

 projection, identical with a far more developed process seen in some lower animals, 

 especially in many of the Bodentia with laminated mallei, and notably in the Musquash 

 (Fiber zibethicus) ; in these extreme cases that projection may readily be taken for 

 the processus gracilis, if the anatomist overlook the fact that its root is not in the right 

 position for the origin of the latter. 



The form of the human processus gracilis is well known. It cannot be seen entire 

 unless taken from a foetal or very young human skull, not only on account of its fra- 

 gility, but also because it actually atrophies to a mere stump before adult life % ; so that 

 after removing a malleus from the temporal bone of a full-grown subject, the anatomist, 



* Henle describes this as " a sharp border " (" Eante "), but he does not mention its sigmoid form. 

 f " On the Structure and Development of the Skull in the Pig," Phil. Trans. 1874. 

 % See Helmholtz, ojo. cit. 

 SECOND SERIES. — ZOOLOGT, VOL. I. 3 E 



