DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 50 
The ossified auditory capsule is seen over the second synchondrosis ; it 1s obliquely 
fixed, large, and full of hills and hollows on this aspect. The supra-auditory tract of 
cartilage has been largely absorbed, but its base was ossified, and that remains as a 
rough crest to the capsule. Below this, in front, the anterior canal (a.s.c.) is seen with 
its ampulla; an oblique rib of bone ascends from the cochlea to the crown of the 
arched canals, the anterior and posterior. This arch and its hinder enlargement 
behind the hollow for the flocculus (jl.7.) is not formed by the posterior canal and its 
ampulla, but by the growth of a tubercle of bone inside that arch, bounding the 
floceular recess behind, as the oblique ridge does in front. 
The meatus auditorius internus (VII. VIII.) is a large archway, between which 
the petromastoid bone swells into the fore part of the deep sulcus for the posterior 
sinus, and for the exit of the 9th and 10th nerves; the hollow for the sinus opens 
below into the foramen lacerum posterius. Behind that opening the lesser hole, 
or condyloid foramen (XII.) is seen in the substance of the exoccipital (e.0.); the 
condyle (cc.c.) is seen behind, the basioccipital (b.0.) in front, and the supraoccipital 
(s.o.) above it. 
The large rough wings of the basisphenoid are seen below the basal section and 
behind the pterygoid bone (py.). 
The inner view of the nasal labyrinth (Plate 20, fig. 5), obtained by removal of the 
perpendicular ethmoid and septum nasi, shows the complex folds of the nasal, inferior, 
upper, and middle turbinals (1.tb., 7.tb., w.tb., m.tb.), and here the ophthalmic nerve (V'.) 
can be seen in its course along the interior of the labyrinth. Below the cribriform 
plate (cr.p.), the right recess of the hindermost part of the nasal cavity is seen 
running by the base where the ethmoidal and presphenoidal regions meet. 
Seventh Stage of the Skull of Evinaceus europeeus ; young; three-fourths grown. 
I have merely figured the outer auditory bones in this, a somewhat more advanced 
a state retained only 
stage than the last, as they are now in a very instructive state 
for a few months longer, after which much absorption and modification of bone will 
take place. 
The outer view of the ear-drum and its chain (Plate 22, fig, 10), shows a condition 
quite comparable to what is found in subadult and adult Marsupials. Moreover the 
annulus (a.ty.), now rapidly strengthening its thickening inner edge, and has there a 
row of small osseous points quite similar to those that are the only rudiments of the 
tympanic ring in the Bird ; that feeble chain of bones is best seen in the Corvidee. 
The processus gracilis of the malleus is several times larger than the manubrium 
(p.gr., mb.) ; it isa strongly ribbed bar, which, appearing in front of its tympanic attach 
ment, there shows a rudiment of the pretympanic hook so large in many Marsupials. 
The body of the malleus is large, and the “ posterior angular process” (p.ag.), behind 
the manubrium, is a semioval convexity. The short crus of the stout end well-made 
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