828 
obvious; it is only necessary for the student 
to recur to less distorted forms of the head at 
once to recognise the reality of the resem- 
blance. 
Should other proof indeed be wanting, the 
manner in which all the cerebral nerves make 
their exit from the cranium would in itself 
offer a convincing argument. In every other 
part of the cerebro-spinal axis the nerves in- 
variably are given off through passages situated 
between contiguous vertebre, which are called, 
from this circumstance, par excellence, inter- 
vertebral foramina ; nay, so sure is this guide, 
that in those instances where the vertebral 
pieces are confused, so as to be otherwise un- 
distinguishable from each other, the position 
and number of these foramina is sufficient to 
indicate the number of vertebre of which the 
part of the skeleton in question originally con- 
sisted, before the pieces composing it became 
permanently anchylosed. Precisely in the 
same manner the nerves derived from the 
encephalon pass out through the interspaces 
between the occipital and parietal vertebrae, 
or between the latter and the frontal; and, 
although from the great bulk of the encephalic 
masses and the number of nerves derived 
therefrom, the passages through which they 
principally escape have been named foramina 
lacera, indicating their size and irregularity ; 
Fig. 438. 
ye N 
He \I 
Z 
ZY 
YH, F 
Izy S\\ ¥ 
KS 
4 SS A 
> V) 
o S 
Gg -S 
Zz Y): 
Z S| 
YZ 
J CA x} 
* a we TY. 
aa ~~ * 
s oH r 
in| ae 
s(a , SH, Ye 
\.| Al ii 
a ly Zt Sit 
Ke BW OL 
Ve C~ ie, 
bt > faa 
Skull of Boa Constrictor. 
they are not on that account less the repre- 
sentatives of the intervertebral foramina pro- 
perly so called. The mere circumstance of the 
channels of some of these nerves being, in the 
human subject and in other Mammifera, cir- 
cumscribed by rings of bone and thus con- 
verted into distinct foramina, to which special 
names have been given by the human osteo- 
OSSEOUS SYSTEM. (Comp. Anat.) 
Fig. 439. 
_ Section of skull of Boa. 
logist, militates in no degree against the grand 
fact that it is between the cranial vertebra th 
all make their exit. _ 
Having given the above general view of t 
composition of the osseous skeleton, a ™ 
difficult task now remains to be accomplished 
viz. to identify and compare with othe 
the individual bones entering into the com: 
position of the osseous system throughout tl 
different vertebral classes, and thus to analyse 
the entire fabric. Various and conflicting im- 
deed are the opinions of different writers oF 
this important subject, of whose names ani 
works an ample list will be given in the Biblio. 
graphy affixed to the end of this article; bu 
to enter into the argumentation of disputed 
points would of course be impossible in ow 
prescribed limits. Suffice it to say, th 
views of the acute and sound-judging Cuvi 
have been principally adhered to, and whe 
occasion has been found to dissent from h 
opinion we have expressed our reasons for 
doing.* 
Bones of the cranium.— Frontals(1). The 
bones in fishes form the roof of the orbit at 
the anterior portion of the cranial box, havi 
in front and behind them other pairs of b 
forming the anterior and posterior boundafi 
of the orbit which correspond with the an 
rior and posterior frontals in Reptiles. In 
Frog the whole of the anterior portion of t 
cranium is made up of a single bone, whi 
entirely surrounds it like a ring or girdle, a 
represents the two frontal bones of Serpet 
* We must here especially nowledge 0 
obligation to Professor Owen, who has most kindl 
placed at our disposal the result of his rch 
concerning the homology of the cranial bones: 
Fishes : his opinions have been introduced in tht 
proper places. D 
