912 
MR. A. FRASER ON THE DEVELOPMENT OF THE 
The cartilages of the Human embryo are very massive (Plate 55, figs. 15 and 16), 
but have otherwise much the same shape as those of other animals. 
On comparing these embryonic parts with those of the adult malleus and incus 
(Plate 58, fig. 40), the derivation of these can be understood at a glance. The head 
of the malleus in the adult Rat articulates with the incus, and from it pass two bony 
processes of considerable size—one has a direction forwards, and soon tapers to a 
point; this may be called the mandibular process, because it is ossified from the 
cartilage (Doran (19) calls it process head of malleus) ; the other, with a direction 
downwards, is the neck. From the lower part of this passes in a forward, downward, 
and inward direction, a long sabre-shaped process, with its edges looking inwards and 
outwards, the manubrium mallei. At the lower part of the neck on its internal surface, 
is the processus muscularis of Hyrtl ; while at the junction of the neck with the 
manubrium are three other processes, one of which looking backwards is very constant 
arid called posterior, another looks outwards, like the processus brevis of the Human 
malleus, and the third looks forwards. Passing from this last to the tapering point of 
the mandibular process, is the free edge of a papery lamina of bone, the extent of 
which depends chiefly on the length of tbe neck; it bears the same relation to the 
mandibular cartilage that the papery bulla does to the tympanic annulus, and it 
developes mainly after the foetus has begun to breathe air, when the tympanic cavity 
expands. The processus gracilis of the adult Human malleus must be formed by the 
atrophy of the mandibular cartilage along the dotted line in Plate 55, fig. 15, the 
head and short neck of tbe Human malleus corresponding to the entire thickness of 
tbe cartilage, tbe lower margin of wbiclr persists as tbe processus gracilis. A study 
of tbe plates illustrating Doran’s (19) paper, wbicli sbow tbe various forms of mallei 
throughout tbe Mammalian orders, will make clear at once tbe morphological signi¬ 
ficance of tbe mandibular process, which is tbe true remnant in tbe adult of tbe 
mandibular cartilage of tbe embryo; tbe whole thickness of tbe cartilage may ossify, 
as in tbe Rat (Plate 58, fig. 40), or its lower margin only, as in tbe Human embryo, 
while there may be all grades of persistence in the thickness of tbe ossified cartilage 
between these two extremes. Tbe adult incus (Plate 58, fig. 40) corresponds in every 
particular save one with its appearance in tbe embryo. When looked at from tbe 
outside, tbe body and the two crura are at once recognised; tbe short crus is but 
little, if at all, inferior in size to tbe long crus; tbe latter stands over the upper 
end of the ossified hyoidean cartilage (tympano-hyal of Flower), seen better after 
the removal of the bulla. The seventh nerve lies behind the tympano-hyal and the 
bulla; its mandibular branch passes external to tbe first-named, and is found with 
tbe greatest difficulty in tbe adult, as also in fine sections of tbe older embryoes, the 
nerves being less conspicuous because of tbe development of tbe surrounding parts. 
It is on looking at tbe incus from tbe anterior view that the only difference is seen to 
exist between its embryonic and adult form. In the adult (Plate 58, fig. 40, B) the 
orbicular apophysis has a pedicular attachment to the apex of the long crus on its 
