DEVELOPMENT OF THE SKULL IN THE MAMMALIA. ) 
that the Mammalian skull was of the high kind, like that seen in many Teleostean 
Vishes, in Lizards, and in Birds. 
It is not so, however, but belongs to the /ow kind, seen in Selachians and Amphibians ; 
and, like theirs, is hinged on to the spine by a pair of occipital condyles. 
Hence the eye-balls are kept far apart, instead of coming very near each other as in 
most Birds, where, often, nothing but a membranous fenestra is found between the 
right and left capsules, and their special rauscular apparatus. 
But the face, as well as the skull, of the Mammal shows marks of excellence, such 
as are not seen in the Sauropsida, even in the higher kinds, as Crocodiles and Birds. 
The great development of the nasal organs is correlated with a most remarkable 
growth of the bones of the upper jaw and the palate to form the “ hard palate.” 
This is found in rudiment even in the Chelonia and in Birds ; but especially in the 
Crocodilia, where, however, its excessive development-—as in certain Edentata, 
e.g., Myrmecophaga—is not dependent upon, or correlated with, any great improve- 
ment in the organs of smell, but has to do with the peculiar manner in which 
these monsters take their prey. 
But that great improvement just spoken of as appearing in the organ of hearing in 
the Mammal has wrought a change in the hinder face that has two most important 
bearings. 
From the first promise of an ear-drum in the tailed Amphibia, to its highest fulfil- 
ment in the noblest of the Oviparous tribes—the Birds that nestle on high (“ Aves 
Altrices ”),—the only element from the visceral arches that is used for carrying the 
vibrations of the air inwards to the organ of hearing ig the uppermost part of the 
hyoid arch—the “ pharyngobranchial” element of the 2nd postoral arch, to speak 
morphologically. 
From the Salamandroids to the Singing Birds, all through the Amphibia and Saurop- 
sida, the Ist postoral arch—which forms both the upper and lower jaw—is only 
segmented once, that is, into an epibranchial and a ceratobranchial element, or 
joint. 
‘The upper piece is specially termed the “ quadrate,” and the lower the “articulo- 
Meckelian;” the one forms the swinging piece, hinge, or pier, to the compound lower 
jaw, and the other its axis or pith, the part which becomes covered with more or fewer 
“investing bones.” 
In these low “ Eutheria,” and also in both the ‘“ Metatheria,” and the “ Prototheria ” 
(Marsupials and Monotremes), the modified visceral rod that runs through the drum 
cavity has two new elements added to the one (single or variously segmented) element 
derived from the hyoid arch. 
This is an apparently sudden change, for we have it in the lowest or teatless 
Mammals; their ancestry, that should show us the earlier steps of the change are, 
unfortunately, all extinct. 
MDCCCLXXXYV. Cc 
