Jan., 1904.] Comparative Chart of Vertebrate Skull. 
53 
The pterotic has been called the squamosal, but the latter arises 
from a separate ossification and is not present in fishes. The tur- 
binals are derived from outgrowths of the bones surrounding the 
nasal chamber and represent true ossifications in IMammals, 
but may remain cartilaginous in the lower groups. The}' are first 
recognized in the Amphibians, where they are merely cartilagin- 
ous protuberances on the bones of the floor and side walls of the 
nasal chamber. 
Characteristics of the different classes : 
Fish. — One occipital condyle. Opercles present only in the 
fish. Some fish have bones which are lacking in others, there 
being a great difference between some of the families in this 
respect. 
Amphibians. — Two occipital condyles ; no trace of supra- or 
basioccipitals. The skull is remarkable for the extent to which 
the chondrocranium is retained and the consequent small number 
■of primary bones. The proolic alone forms the auditory capsule 
in the frog, the other otic ossifications not being developed ; in 
the Urodels an opisthotic is added. 
Reptiles. — One occipital condyle. The transverse is pre.sent 
in all reptiles, except the turtles, and in no other vertebrates. 
The zygomatic arch, formed by the quadrato- jugal and the jugal, 
is wanting in the Ophidians. In turtles there are no teeth, and 
the basisphenoid is the only one of the sphenoidal bones pre.sent. 
Of the otic bones the prootic is always distinct, the epiotic is 
fused with the .supraoccipital, while the opisthotic (free in tur- 
tles) is usually united to the exoccipital. 
Birds. — One occipital condyle. The bones of the cranium fuse 
■early so that the sutures between them are obliterated. Teeth 
are lacking in modern birds. The anterior end of the parasphen- 
oid forms the rostrum and the posterior the basitemporal. 
M.-vmmals. — Two occipital condyles. The lower mandible 
articulates with the squamosal and is composed of five elements 
on each side, as the articular has been taken into the middle ear 
to form the malleus. The quadrate has gone into the ear and 
become the incus. The stapes is derived from the hyomandibu- 
lar and from some membranous elements. 
EXPI,.\N.'\.TION OF PL.\TES III .\ND IV. 
S=Salmon; F=Frog; U=Urodele; I/=Lacerta; 0=0phidian; T=Turtle; 
A=Alligator ; D=Duck ; P=Pigeon ; C=Chicken ; H=I)og ; R=Rabbit ; 
IM=Man. In the first column after the name of the bone, c=cartilage bone 
and m=menbrane bone. 
