312 
MR. W. K. PARKER ON THE STRUCTURE AND 
lently illustrated by the late Dr. Eschricht (“ Ni Tavler til Oplysning af Hvaldyrenes 
Bygning, udferte til utrykte Foredrag af afdede Etatsraad Dr. D. F. Eschricht Copen- 
hagen, 1869. Edited by Professor Reinhardt, plate ii. figs. 1-3). 
The well-marked granular territories that at first invested the primordial skull and 
face are now largely ossified, and these ossifications are massive in relation to so small a 
skull. As in the strong-legged “ Herbivora ” generally, and in the “ Aves prsecoces,” 
the development before birth and before hatching is very rapid, so that they are strong 
and in good liking at their first appearance. Moreover, the primordial parts are 
undergoing endostosis at many’points, and from this time the bony metamorphosis takes 
place very rapidly. If this skull (Plate XXXIV. figs. 1-7) be compared with that of 
the Bird (“Fowl’s Skull,” Plate lxxxiv.-lxxxvii.), it will be seen that the premaxillaries 
(j px .) do not reach to the end of the snout, instead of projecting beyond it, and they do 
not send a nasal process between the nasal bones up to the frontal. Here, in the 
Mammal, the maxillary is by far the largest bone, and, with the linking malar and 
zygomatic spur of the squamosal, forms a strong subocular arch, one pier of which is 
formed by the maxillary and reaches near to the nostril, whilst the other pier is formed 
by the supratemporal and stretches over the auditory capsule to the occiput (Plate 
XXXIV. fig. 1 z.sq.). This sigmoid, trilobate temporal (squamosal) bone, besides 
creeping over the infero-lateral wall of the cranium by its squamous part, clamping the 
outer wall of the ear-capsule by a long falcate process, and perfecting the great facial 
yoke (zygoma), also takes in a new relation ; it articulates with a well-differentiated 
secondary mandible ( d ). This is distinctively Mammalian ; for in the highest Sauropsida 
(the Bird) the primordial and secondary mandibles have an equal development, and are 
permanently combined as the free arch of the mandible, the large “ pier ” of which 
is merely the hugely developed head, neck, and shoulder of the first mandibular rod. 
In this stage of the Mammalian skull we catch the equivalence of these primary and 
investing parts ; but the new hinge is formed already, and the primary bar, now at 
its highest relative development, shows no sign of segmentation into a pier (quadrate) 
and a free arch (articulo-Meckelian). By the time of birth, the whole of the large 
succulent rod of cartilage which runs along the inside of the lower jaw (fig. 7, d., mk., m.) 
and coalesces largely with its fellow in front will have shrunk up into a delicate fibrous 
band, leaving a small bony style (processus gracilis) to the arrested upper part of the 
rod*. A bony ring is growing round both the preoral and the first postoral clefts; 
these are the lacrymal ( l .) and the tympanic ( ty .) ; the first of these has an outer facial 
development, and is not hidden in the orbit as in Man. The nasal, frontal, and parietal 
bones (n., f., p.) form a regular double series ; they are only equivalent to the inner 
layer of the scutes seen in the same region in Ganoid Fishes ; yet they are very thick, 
the thickness depending upon the free development of connective (indifferent) tissue 
between the cutis and the primordial skull. The fontanelles are still wide open ; but 
* In the figure (Plate XXXIV. fig, 7, cl.mlc.) the primary rod is cut through, and the mandible detached 
from its new hinge these parts will he described more in detail from the figures of sections. 
