SKELETON. IOI 
position. Thus the petrosal, instead of forming part of the side wall, is carried to 
the floor of the brain cavity and the squamosal forms part of the lateral wall. 
The roof of the brain cavity is largely formed by parietals and frontals. (In some 
whales, denticetes, the supraoccipital and interparietal extend to the frontal, pre- 
venting the parietals from meeting.) The frontals may be distinct or they may 
fuse. In many ungulates they bear horns or antlers. In cattle, antelopes, sheep 
and goats (cavicornia) a strong bony process or horn core is developed on each 
frontal, and this is covered by a cornified epidermis and persists through life. The 
antlers of the deer differ from horns. Each year there is an outgrowth of bony 
material, covered by a richly vascular skin, from each frontal bone. This grows 
with remarkable rapidity, and when its full extent is reached, the skin (‘velvet’) is 
lost, leaving the core alone. After about a year resorption takes place at the base 
so that the antler is soongost, to be replaced by a similar but larger one in a few 
weeks. 
The nasals lie above and behind the nares. The margin of the upper jaw is 
formed by premaxillaries followed by the maxillaries which ossify from several 
centres, difficult to homologize with distinct bones in the lower vertebrates. The 
inferior turbinals fuse to the inner surfaces of the maxillaries. Premaxillaries and 
maxillaries may fuse or they may remain distinct. They have broad palatine 
“processes on the oral surface, these meeting in the middle line and forming the 
anterior part of the hard palate, with frequently one or two incisive foramina 
for the passage of the nasopalatine nerve between them. The choanz are usually 
behind the palatine bones which form the rest of the hard palate, but in some eden- 
tates‘and whales the pterygoids form part of the partition between the narial pas- 
sages and the mouth cavity. 
The ingrowth of the hard palate has forced the vomer from the roof of the mouth 
to a position just ventral to the anterior part of the cartilage of the nasal septum. 
In the monotremes there is a ‘dumb-bell 
bone’ in front of the vomer (p. 69). A 
lacrimal bone always occurs at the inner 
side of the orbit and the zygomatic forms 
the external wall of that cavity. 
The lower jaw articulates directly with 
the squamosal without the intervention of 
a quadrate (see ear bones, p. 74). Its 
halves may unite in front by ligament or 
z i Fic. 105.—Hyoid of rhinoceros (Ate- 
by complete anchylosis, It is usually Jodus). ac, anterior cornu; b, body; ¢, 
described as consisting of a pair of den- ceratohyal; e, epihyal: pc, posterior cornu 
: 7 ]). 
taries, but there are several centres of ossi- (thyrohyal) 
fication and a splenial and possibly a coronoid may be recognized. The angulare 
is apparently the tympanic, while the articulare of lower vertebrates is the malleus. 
A remarkable feature in development is an enormous cartilage at the posterior 
angle of the jaw, the dorsal side of which forms the condyle for articulation with 
the glenoid fossa. 
The hyoid apparatus varies. As described above, the hyoid is connected above | 
with the otic region, below with the first branchial. The part connected with the 
‘ 
