OSSEOUS SYSTEM. (Comp. Anat.) 
(fig. 438, 1) united together. In the Siren 
and Proteus, however, the principal frontals are 
divided as in other Reptiles. In all Birds and 
Mammalia these bones become at an early 
period confused with the anterior and posterior 
frontals and ultimately with each other, so as 
to form but one piece, the os frontis of man; 
nevertheless, even in the human fetus, they are 
separated by a suture which, in the lower 
Mammalia and also in the human subject, is 
not unfrequently persistent to alate period oflife. 
The anterior /rontals (2) in the osseous 
Fishes bound the orbit anteriorly. Between 
these bones pass out the olfactory nerves, but 
they are not always distinctly recognisable, 
being occasionally permanently cartilaginous. 
In Reptiles these bones are generally distinct, 
but in Birds and Mammalia they coalesce with 
the preceding. 
he posterior frontals (4) form the posterior 
margin of the orbit, and are present in Fishes 
and the Reptilia, but in Birds and Mammifers 
they are no longer recognisable as distinct 
bones. 
The parietal bones (7) are placed behind the 
frontals; but these bones do not always touch 
each other, being separated, especially in Fishes, 
by the interposition of an azygos bone from 
which projects the occipital spine, which is 
frequently, more especially in Fishes, of very 
good size: this impair bone, the interparietal 
of some authors, is in reality the representative 
of the superior occipitals of Cuvier (supra- 
occipitals, Owen ;) (8) and in some Fishes, es- 
pecially in the Si/uri, where the parietals are 
totally wanting, their place is supplied by the 
enormous developement of this element of the 
skeleton. 
The external occipitals (9) contribute to form 
Fig 440. 
Section of the skull of Turtle ( Testudo Myas). 
829 
the lateral portions of the occipital region of 
the skull, in conjunction with two other pieces 
called ~ 
The /ateral occipitals (10), which partially 
bound the foramen magnum. 
The inferior occipital or basilar bone (5) is 
that which invariably is articulated to the body 
of the first cervical vertebra, but occasionally 
in Fishes there are two additional articulations 
connecting the cranium to the spinal column 
formed by the lower portions of the lateral 
occipitals. All these elements of the so-called 
occipital bone of the human cranium remain 
permanently distinct in Fishes and Reptiles, and 
even in the feetal condition of Birds and Mam- 
mals are more or less recognisable; but they 
soon coalesce into one large piece that enters 
largely into the formation of the cranial box, 
and constitute the first or occipital cranial 
vertebra, as has been already seen. 
The sphenoid (6) invariably occupies the cen- 
tral portion of the base of the cranium, and in 
Fishes and Birds is prolonged anteriorly into a 
lengthy process which passes beneath the inter- 
orbital septum, which,in these classes of Verte- 
brata, remains most frequently membranous. 
The alar bones (11; ali-sphenoid, Owen,) 
represented in the human subject by the greater 
ale of the sphenoid, are in reality distinct 
elements of the cranium, and are recognizable 
by several important characters, especially by 
their position being joined by suture to the 
oo frontral, and, conjointly with the latter 
ne, to the temporal. Moreover, through 
these bones the two posterior divisions of the 
fifth pair of nerves always pass out from the 
skull. In Fishes and Reptiles they are im- 
portant pieces and quite detached from the 
sphenoid. 
The squamo-temporal bones, Owen (mastoid 
bones, Cuv.: 12) in Fishes are manifestly the 
representatives of the bones so named in Rep- 
tiles. They contribute in conjunction with the 
posterior frontal, and occasionally with the alar, 
to furnish the articular surface that sustains the 
first bone of the palatine and tympanic appa- 
ratus, or, in other words, of the masto-tem- 
poral (23). 
The petro-temporal bones, Owen, (13) are in 
Fishes placed between the mastoid, the lateral, 
occipital, and the alar bones. They are gene- 
rally of small size, but occasionally, as in the 
Gadide, very largely developed, descending to 
reach the inferior occipital and the sphenoid. 
On the other hand, they are frequently entirely 
wanting, as, for instance, in the Pike, the Carp, 
and the Eel. 
In all the Reptilia the petro-temporal bones 
are recognizable as distinct pieces forming part 
of the cranial box, and become interesting, 
inasmuch as it is in them that the auditory 
apparatus is lodged. 
In Birds and Mammalia, however, the 
petrous bones become at an early period 
inseparably soldered to the other pieces, form- 
ing the so-called “ temporal bone.” 
' The ingrassial bones (14), as they have been 
named by Geoffroy, are, in the human subject, 
regarded as portions of the sphenoid, although 
