702 MAMMALIA, 
The sul consists, as in all the higher Vertebrates, of two 
sets of bones,—cartilage bones preformed in the cartilage of 
the original gristly brain-box and its associated arches, and 
membrane bones developing in the investing membrane and 
not preformed in cartilage. (The names of the membrane 
bones are printed in italics.) 
We have already noticed the chief characteristics of the 
mammalian skull, such as the usual persistence of sutures, 
the two condyles, the bony 
palate, the fusion of the 
periotic bones, the articu- 
lation of the mandible with 
the squamosal, the fusion 
of the parts of each ramus 
of themandibleintoa single 
bone in the adult, and the 
three ossicles of the ear. 
The foramen magnum is 
bounded by the basioccipital 
beneath, the exoccipitals on the 
sides, the supraoccipital above. 
The exoccipitals form most of 
the occipital condyles, but the 
basioccipital contributes a small 
part. In many Mammals the 
exoccipitals alone form the con- 
dyles. From each exoccipital a 
paroccipital process descends, 
and is applied to the tympanic 
bulla—a dilatation at the base 
of the ¢yspanzc bone which pro- 
tects the external auditory tube, 
Along the roof of the skull 
lie the supraoccipital, the zxder- 
rabbit’s skull. ; : 
W., Anterior nostril; PAZX., premaxilla; MA., ia tage ue vel a the fron- 
nasal; FR., anterior part of frontal; JLX., tals, and the zasaés. 
posterior part of maxilla; /., anterior part On the very front of the skull 
etugsl Pepe supraorbital eee oh on are the premaxdlle, bearing the 
tal; -» posterior part of frontal; //., ++ ‘ - 
posterior end of jugal protruding below. oO IneIsOr teeth, Behind each pre 
matic portion of squamosal (Z.SQ.); PA., maxilla is a maxilla, bearing 
parietal; AM., external auditory meatus; the premolars and molars; be- 
SO., supraoccipital ; /P., interparietal ; SQ., hind this, along the z gomatic 
squamosal, 2 § ek) 
or temporal arch projecting be- 
neath the orbit, is the jugaZ or malar, which unites posteriorly with 
the sguamosal. This zygomatic arch bridges over the deep temporal 
fossa behind the orbit, and serves for the insertion of muscles, and its 
‘*squamoso-maxillary” structure occurs outside of Mammalia in the 
Fic. 384.— Upper surface of 
