AMJIALIA VEirrEBRATA— VERTEBIIATED ANIMALS. 
2.3 
for a lon*^ time ixnconsoUdated» and llicrvi appears botween them a quantity of maUer 
purely gelatinous, capable of being dissolved by boiling water. The oxlrcmitics, while 
*<^parated, aro called epiphyses^ while iliat in the body of tho bone is termed dlnphif}.is. 
In the flat bones, the centres of ossification may be compared to sans, of which the bony 
fibres are the rays, rendered visible through the semi-transparent cartilage by their 
opaque whiteness. These centres vary their appearances in dilTcrent bones : in the 
round bones they resemble small grains or nuclei, but in the angular bones they a.ssurao 
a great variety of forms and positions. 
When the fibres of one centre have advancod so far as to come every whore in con- 
tact ^Yith those next to thetn, the bones arc then only separated by sutures, which 
may afterwards be more or less promptly effaced. Some of these fibres turn aside to 
the right and left, and thus produce the appearance of latticc-worh 5 while new' strata, 
placed above and below the former, cause the texture of the bone to assume a lamel- 
lated aspect. 
We are in the habit of considering as single bones, all those of which the different 
parts ossify and unite in youth, as the vertebra?, the occipital and frontal bones; 
while wc consider those that do not form .a union with the neighbouring bone.s until 
an advanced period of life, as distinct. Thus the frontal bone, which sometimes 
remains separate fromtlio parietal bones to a very old age, is regarded .is a distinct 
bone ; while at tho same time it is composed of two parts, which frequently remain 
separate until the age of thirty or forty. 
Ossification i-s not found to proceed with an equal rapidity, whether wc consider it 
in each kind of animal, or in the different bones of the same animal. In !\Iau, and all 
other Mammalia, wo observe that the bones of the internal oar are not only first 
ossified, but that they surpass all other.s in density, and in tho quantity of calcareous 
phosphate they contain. Tims, tho bone of tlm cavity of the tympanum in the 
Cetacea, but particularly in the 'Whale ,md the Cachalot, is superior to marble in 
hardness and density. Its section appears equally homogeneous, and exhibits no vestige 
of fibres, luttice-worJt, or vessels. On tho contrary, other bones arc very slow in 
acquiring the consistency they ultimately possess. The epiphyses, for example, do not 
ossify until long after tho bodies of tho bones to w'hich they belong. Finally, there 
are some cartilages, which, in certain classes of animals, never admit a quantity of 
calcareous phosphate sufficient to rondcr them completely bony ; such as tho cartilages 
of the ribs, and tho lai^nx. It is certain, therefore, tliat there are several cartilages 
wliich arc never converted into bones, although there is no bone which did not for- 
merly exist in ihc state of cartilage; yet, there is a general tendency in all gelatinous 
parts to receive calcareous matter, as tho tendons, and several white parts, ossify with 
greater facility than tho others. Idic same differences which exist in this respect 
between the several bones of the same species, aro also found to exist between species 
and species, on comparing the entire skeleton. 
Wc not only find tfiat the bones of an animal arc slow in arriving at tho degree of 
hardness which belongs to them, in proportion to the period of the growth of the 
animal ; but we further know, that there are some animals in which ossification is 
never complete, and whose skeletons arc always cartilaginous. This, is the case with 
Sharks, Rays, Sturgeons, and all those Fishes which are thence called cartilaginous, 
or Chondropterygii. Although tho bones of llie othL*r Fishes, and of many Reptiles, 
attain a greater degree of hardness, they still, however, jirescrve much more flexibility, 
^nd retain a far greater proportion of the gelatinous substance, tlmn the bones of 
animals having wai'm blood. They grow, therefore, during the whole period of their 
existence ; because it is cartilago only th.at can grow. On the contrary, when onco 
the bones have attained their proper degree of hai'daeas, their dimensions cannot alter; 
^d tho animal can only increase in thickness. At this period, the animal economy 
commences a retrograde movement, and tho first steps arc made towards old ago and 
decrepitude. 
Animals differ greatly in respect to the texture of tho bones, and the cavities of 
■'Various kinds formed within them, as well as in the rapidity of ossi.fication, and in the 
proportions which the fionstituent parts of bone bear to each other, [n Man, tho in- 
ternal texture of tho bones is very fine. Tho lamiuDD of their spongy substance arc 
»maU and close; and where this loxluro is most unlike lattice-work, it exhibits long 
and dcUcato fibres. lu Quadrupeds, the texture of the bones is in general coarser; 
*0 the Cetacea, it is more loose, the cells arc larger, and the larainre winch form them 
niuch broader. It is easy to distinguish their external fibres, which in tho juws and 
ribs of Whales and C.’achalots may be rendered as evident, by long maceration in 
""^tor, as tho fibres of lialf-dccayod wood. With respect to size, however, they seem 
bi bear no relation to the magnitude of tho animal to which they belong. The bones 
Birds aro of a slender, firm, and elastic nature, and seem formed of laminm soldored, 
one over the uUier. Tho bones of Reptiles and Fishes arc in general more bomo- 
K<‘neous, and the cUcareous particles seem mure uniformly distributed throughout tho 
l?‘?latinous substance. This observation appears the more stinking as wc approach the 
cartilaginous Fi?hos, in which the gelatinous substance completely overcomes, and ap- 
pt'ars to coneoah the phosphate of lime. 
Several animals have no largo mcdull.'vry cavities even in their long bones. There 
none in tho Cetacea and Seals. Caldosi and Cuvier have long remarked the same 
^biig in respcet tu ihe Tortoise. The Crocodile, iiowcver, has these cavities very distinct. 
In some bones wo find other cavitiu.s, called amuse.% which contain no marrow. 
I ‘‘^y all communicate, more or less directly, with the exterior of the body. Mim lias 
‘‘’•uses In ti»e frontal, sphenoid, and ma.xilbry bones of the skull. In several Mam- 
theso siiuLses extend much further backwards, and penetr.ato through a great 
p.irt of the body of the cranium. In tlio Hctg they proceed as far as the occiput; 
^nd it is these wliich swell so singularly flic cranium of the Elephant, and which 
superficial observers arc ajd to mistake for an extraordinary development of the brain. 
Oxen, Goats, and Sheep, those sinuses extend even into the centres of the horns, 
le Gazelles arc tho only animals with hallow liorns, liaving the nucleus of their 
urns solid or-spongy without any large cavity. 
Other sinuses exist m tho temporal bones ; these communicate with tho cavity of 
tympanum. 1 hose arc particularly extensive in IJircU, and occupy as much space 
^ the nasal sinuses do in Quadrupeds. Tliey produce the same effect on the cranium 
® the Owl, as tho other kinds of siiiu? produce on that of the Elephant. 
Tho growth of the horns of tho Deer present singular phenomena, which will bo 
described in tboir proper place. 
The blood of tlio Vertebrata is always rod; and it appears to possess 
a peculiar composition, fitted to preserve that energy of sensation and 
nmscular vigour observable in this division of animals. These properties, 
liowcvcr, greatly depend upon the degree of perfection in which respira- 
tion is performed; and this circumstance gives rise to the subdivision 
of the Vertebrata into four classes [Mammalia, Birds, Reptiles, and 
Fishes.] 
The external senses are always five in number; and they reside in two 
eyes, two ears, two nostrils, the integuments of the tongue, and those of 
the whole body. Certain species seem [at first sight] destitute of eyes. 
But this is only apparent, as all the Vertebrata have two eyes composed of the 
same essential parts as those of Man. The only apparent exceptions aro the Mus 
iyphlus, or Blind Rnl, where the eyes arc concealed under the skin; and tho Fish 
called Cohitis anublapSy whore the same eye, having two pupils, appears double. 
The nerves reach the marrow through tho liolos of the vertebrae and 
of the skull; and they all appear to become incorporated with it. After 
interlacing its filaments, the marrow expands itself in forming the various 
lobes of ^Ylnch the brain is composed, and terminates in two arched 
masses called liomisphero.s; the volume of w'hicli is [sometimes] propor- 
tioned to the degree of intelligence possessed by the animal. 
Most of the nerves of the trunk and of the limbs arise from the spinal marrow, 
whoncG they are distributed, and through their moans sensation and motion are trans- 
mitted to the several parts of the body. “When any portion of the spinal marrow is 
compressed or divided, all those parts to which nerves are transmitted, arising from 
the portion of tho spinal column situate below the part compressed, are immediately 
paralyzed and dq»rived of sensation and motion. In some species remarkably tena- 
cious of life, a remnant of consciousness will remain, oven after the entire separation 
of tho brain and spinal cord. If tho head of a serpent bo removed, and .shortly after- 
wards tho .skin of its tail he punctured by a sharp instrument, the headless trunk will 
turn instinctively to defend the. part attacked. 
The internal structure of the spinal cord is well exhibited on making a section of 
tlie spine of a Carp. Its spinal cord is composed of six columns running parallo), 
and arranged symmetrically round a central canal filled genorally with fluid. The pair 
of columns situate behind aro appropriated for sensation, and tho two iu front for 
voluntary motion. Fibres arc transmitted from each side ; these unite and form nerves, 
yet the fibres still retain thinr characteristic functions. The nerves of sonsatio.n have 
small ganglions or knots near the central column ; and tho whole are formed into one 
system by the sympathetic nerve, which is parallel to the spine, and passes ncai- it on 
each side. 
There are four principal portions of the Human Brain — 1, the Medulla oblongata; 
2, the Corcbcliura; 3, tho Cerebrum; and 4, the Optic tubercles. Besides these, there 
are many intricate parts, which wc shall not attempt to describe in this outline. 
J . The MuDULiiA OiiLONCATA is that part of the brain which forms the immediate 
continuation of the spinal cord. It appears to contain the portion most csj*e«t.ial to 
life and consciousness. Every other part of the brain may be successivoly taken away, 
at every mutilation tlie sphere of vital action may be diminished; yet, if llie McdulUi 
ohlonpnta be preserved entire, nay, oven if that minute portion near tlie origin of 
tho fifth and eighth nerves be uninjured, the animal will still exhibit marks of instinct 
and sensation. Upon removing the cerebrum, cerebellum, and tubercles of a living 
hodge-hog, M. Magendie found that tho .animal was rendered blind; yet it remained 
acutely sensible to smell, taste, or bodily punctures; and its powers of locomotion were 
unimpaired. Infants are sometimes born acephalous.^ that is, without a brain, and 
possessed only of the Medulla oblonpatay nerves, and spinal cord. When they sur- 
vive for a short time after birth, which does not often ha])pen, they always possess 
sensation and motion. Yet their brain only resembles that of tho iMollusca, such as 
the snail or tho oyster. One infant, described by Mr Lawrence, survived four 
d.ays. “ Tlio brain and cranium of this infant were deficient, and the basis of the 
latter was covered by the common integuments, except over the foramen magnum 
(or that hole in tho skull which coinmunicatc.s with the vcrLcbr.al column), where 
thero existed a soft tumour, about equal in size to tho end of the thumb. Tiie 
smooth membrane covering this was connected at its circumfiinmeo to the skin. The 
child, as U generally the case in such instances, was perfectly formed in all its other 
purls, and had attained its full size. It moved briskly at first, but niinained quiet 
afterwards, except when tho tumour was pressed, which occasioned general convul- 
sions. It breathctl naturally, and w.is nt)t observed to bo deficient in warmtli, until 
its powers declined. From a fear of alarming the mother, no attempt was made to 
see whether It would tako the breast; but a little food was given it by tlje hand.” 
From those inslancos, it appears that the brain is not essentially necessary to tho 
performance of tho ordinary instinctive functions of an animal; but that ills tho 
Medulla oblongata which forms tho essential organ. If tho head of a tortoise or frog 
be cut off, sensation will remain cither in the separated head, or in the headless trunk, 
according as the section has boon matle above or below this vital part. It is a curious 
fact, that the usual effects of an emetic are prevented by pressure on the Medulla 
oblongata y or vomiting is instantly arrested, if it has already commenced. 
2. The CEiiEnEr,i.CM, or little brain, is the tviberclo or tubercles arising from the 
expansion of the hinder portions of the spinal marrow. It would thcroforo appear to 
bo more especially designed for sensation. In Man, the Cerebellum is composed of 
two largo hemispheres, connected togethur by the vermiform processes, so as to form 
one structure, being composed of a wliile nervous substance, enveloped in a uniform, 
covering of gray matter. 'When this part of the brain is injured, the animal is affected 
with a kind of giddiness, by which it appears to be hurried forwards. Iu attempting 
