86 
MR. W. K. PARKER OK THE STRUCTURE AND 
squamosal; the malleus (ml.) has been dislocated from it, and also the new ramus 
from its zygomatic or glenoid facet (figs. 3 and 6 ; in the former these parts are seen 
from the outside, in the latter more magnified figure, from within). The superficial 
secondary mandible (cl.) is lesser than the deep primary rod (mk.) ; it is applying itself 
to the upper and outer face of that rod, and in front is composed of two delicate 
tracts of bone, the inner and lower of which (sp., line too short) corresponds to the 
separate splenial of the Ovipara. But the main part of the ramus is a thickish 
lanceolate tract of hyaline cartilage; an “ inferior labial,” part of which tract has 
already become segmented off to form the glenoid facet. 
Meckel’s cartilage (mk.) has united with its fellow in front, and the two have an 
azygous rod in front of them, a hasimandibular (h.mn.). The whole rod is sinuous, 
and thickens gradually backwards; the last fifth is behind the “ramus,” and is the 
part which becomes the malleus (ml.). Then the rod is arched upwards, and thence 
swells into a head, or articular portion, with a saddle-shaped condyle ; from the head 
there arises a long and a short process—internal and posterior angular processes, 
which become the manubrium mallei ( m.ml.). The long process forms an acute angle 
with the main rod, and ends in a slight dilatation in the middle of the developing 
membrana tympani ( m.ty .), in the fore margin of which a slight arc of bony cells is 
seen, the annulus (a.ty.). Under the proximal part of the rod a fine tract of 
membrane-bone is seen, the first appearance of bone to form the malleus (= the 
ectosteal “ articulare ” of the Ovipara). 
The quadrate or incus (i.) is a quadrilobate segment of cartilage, binding against 
the malleus by the two front lobes, articulated to the tegmen tympani by the postero- 
superior, and applying its inturned postero-inferior lobe, which has an orbicular facet at 
its end, to the head of the stapes. The latter part (st.) is oval in its base or proximal 
part, and then its short solid stem dilates in an orbicular manner to articulate with 
the incus. 
That is the pharyngohyal; the epihyal is seen from below as a small lobe of car¬ 
tilage, confluent with the ear-capsule, and forming a small bridge for the facial nerve 
to pass over (fig. 1, e.liy., YII.). The next segment is the ceratohyal (fig. 5, c.hy.), it 
is fibrous above, and instead of having an extra segment, above, and a hypohyal, 
below, as in most Mammals, there is but one piece altogether. The basal piece 
(b.li.hr.) is also very rudimentary, being a bent [J-shaped rod, with very short 
continuous crura (t.hy.). 
Now in such an aberrant and feebly developed face as this, we can the better com¬ 
pare the Mammal with the Bird. In the latter the epihyal ( = stylohyal) cartilage is 
also short; it does not, however, form an adhesion with the auditory capsule, but 
with a slender outgrowth from the neck of the columella ( = stapes) (see “ Bird’s 
Skull,” Part II., Trans. Linn. Soc., ser. 2: Zook vol. i., Plate 20, figs. 7, and 8-11). 
That outgrowth—the infrastapedial band—is represented in Fishes by the interhyal, 
a segment which re-appears in the Mammal, and becomes wrapped up amongst the 
