DEVELOPMENT OF THE SKULL IN THE PIG. 519 
Oviparous Vertebrata, where the fusion of the periotic capsule with the skull proper is 
the greatest. Here, in the Pig, the bony deposits are formed much as in Man (see 
Huxzey, ‘ Elem. Comp. Anat.’ pp. 147-156). A description such as that quoted above 
serves almost equally well for both types. Looking at the inner face of the capsule 
(figs. 3 & 4), we see a creeping endosteal patch, which surrounds the ‘ meatus 
internus,” runs under the,fore part or apex of the cochlea, and has found its way 
supero-posteriorly to the junction of the anterior and posterior canals (@.s¢., p.sc.). 
Seen from the outside (fig. 5, pro.) the same bony tract is seen above and in front of 
the “ fenestra ovalis” (fov.), below which it forms a sudden hook-like bend, which turns 
forwards, passing into the tract seen on the inside of the cochlea: this is the ‘* prootic” 
ossification, 
On the inside (fig. 5) a small hook of bone is seen in front of the ‘foramen lacerum 
posterius” (8); this is a spur sent round the back of the capsule from the outside, 
and the plate of which it is a process is seen from that aspect (fig. 5, op.) covering the 
most bulbous part of the cochlea, the ‘* promontory” (pv.). ‘This is the “ opisthotic 
bone ;” it sends forwards and downwards a long hook, which binds behind the hook of the 
prootic, beneath the apex of the cochlea. Another process of the opisthotic runs 
between the fenestra ovalis and fenestra rotunda (f.ov., fv.) close in front of the head 
of the styloid cartilage (st.h.). Above the head of the styloid, and below the hinder 
end of the tegmen tympani, a smaller spatulate scute has appeared; this is the mas- 
toid proper, or “ epiotic.” Behind this little bone the auditory mass is much contracted 
in the Pig, this part of the capsule being strongly clamped by the squamosal and im- 
pinged upon by the exoccipital (e.0.), where it gives off its ‘* paroccipital process ” 
(p.oc.). The “ epiotic” centre will, moreover, ossify the true mastoid region; although 
it arises in a more forward position, it is less than that of Man (see HuXuey, op. cit. p. 154, 
fig. 61, ep.o.). In the vertical section (fig. 11) the prootic and opisthotic centres are cut 
through, each at two places, the first (pi'o.) above the stapes (s¢.) and inside the cochlea 
(e/.), and the opisthotic appears below the stapes and in the substance of the promon- 
tory (pr.). On the outside the semicircular canals are seen (a.8¢., /.sc., p.sc.) imbedded 
in solid cartilage. The structures of the “ middle ear” have now acquired their almost 
full metamorphosis; these are enclosed in a large imperfect ring of bone, the tympanic 
(figs. 1 & 2, ty.). This bone is now becoming very thick, and its breadth has greatly 
increased ; butas yet there is no bony meatus stretching outwards beyond the membrana 
tympani (i.¢.). It will be seen in the lower view that there is an additional bone 
clinging to the inner edge of the tympanic; this wedge and two smaller ossicles which 
I shall describe in the next stage are the feeble counterparts of the auditory “bulla” of 
the ‘* Felidie” and their congeners *. 
* On the subject of the auditory “bulla” of the Carnivora, see Professor W. H. Frowsr’s very valuable 
paper “On the Value of the Characters of the Base of the Cranium in the Classification of the Carnivora” &c., 
Proc. Zool. Soc., Jan. 14, 1869, p. 4. Whilst Professor Huxiny’s ‘ Elements’ was going through the press, L 
showed him the bulla of the new-born Lion’s whelp, a thin spoon-like lamina of {rue hyaline cartilage growing 
outwards from the inferior edge of the opisthotic region. oon after this, Professor Rotrrsron presented me 
