Francis Lieber.

Library of universal knowledge. A reprint of the last (1880) Edinburgh and London edition of Chambers' encyclopaedia, with copious additions by American editors (Volume 13) online

. (page 126 of 203)
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than in tiie sturgeon, overlapping each other, and being fastened together like tiles by a
peg of one entering a socket in the next, and conversely.

In tiie armadillo the dermal bones are small, usually five or six sided, smooth
internally, and variously sculptured externally the pattern, however, being constant in,
and characteristic of, each, species. They are united together at their margins by rough
surfaces, and collectively resemble a tesselated pavement. To allow of the requisite
movements of the trunk of the armadillo, which have the power of rolling themselves
into a ball, a certain number of transverse rows are interposed, having an elastic yielding
attachment with one another, and with the anterior and posterior fixed parts of
the trunk-armor; and by this arrangement, the head and limbs can be withdrawn
beneath the central case, by the action of strong subcutaneous mu.-cles. In the colossal
extinct armadillo (the glyptodon) the trunk-armor was not divided by bands, but was
composed of one immovable piece, covering the back and sides an arrangement by
which the dermo-skeleton would afford increase protection against falling timber, the
attacks of other animals, etc.

The splanch no-skeleton is at first sight less apparent than the dermo skeleton. In
most air-breathing vertebrates the larynx, trachea, and bronchial tubes contain a car-
tilaginous framework which sometimes becomes ossified; in fishes, and in the batra-
chians in the tadpole state, the gills are supported upon a cartilaginous or osseous frame-
work, developed independently of the vertebral skeleton; and in many mammals the
heart contains a bone that serves as a support for its muscular and liga'mentous fibers.
If to these parts we add the so-called "sense-capsules" the bony crip which is found in
the outer coat of the eye in many birds and most fishes; the hard bony envelope which
surrounds the internal ear, and which subsequently, as the petrous portion of the tem-
poral bone, becomes incorporated in most vertebrates with the neuro skeleton; and the
turbinate bones of the nose and the teeth, we have the principal parts of the splanchno-
skeleton. The selero-skeleton requires no further explanation than that which has been
already given ; and we therefore proceed to what may he called the skeleton proper the
neuro-'skeleton.

From the nature of the subject it is impossible to avoid the introduction of a con-
siderable number of technical terms, which will probably be new, and will sound some-
what harshly to many of our readers; and as few writers can popularize a difficult
subject more successfully than prof. Owen himself (unquestionably the greatest osteolo-
gist of the present age), we shall for the most part follow the history of the neuro-
skeleton, which he drew up for the benefit of general readers in The Circle of the
Sciences. A thoughtful examination of the skeleton of any vertebrate shows that it is



Skeleton.



544



arranged in a scries of segments, following and articulating with each other in the
direction of the axis of the body, from before backward in brutes, from above down-
ward in man. Each complete segment, called a "vertebra," consists of a series of
osseous pieces arranged according to the plan shown in Figs. 2 and 3, so as to form a
bony hoop or arch above a central piece for the protection of a segment of the nervous
axis; and a bony hoop or arch beoeath the central piece for the protection of a segment
of the vascular system. The upper hoop, N, is called the "'neural arch" (Gr. neuron, a
nerve), and the lower hoop, H, the "hemal arch" (Gr. hcema, blood); while their com-
mon center, C, is termed the centrum. The neural arch is formed by a pair of bones,
7i, n, called " neurapophyses" (Gr. apopliysis, a projecting part or process), and by a
bone, us, sometimes clef t or bifid, called the "neural spine;" it also sometimes includes
a pair of bones, d, d, called " diapophyses" (Gr. dia, across). The hemal arch is formed
by a pair of bones, pi, called "pleurapophyses" (Gr. pleuron, a rib); by a second pair, h,




FIG. 1. TYPICAL VERTEBRA

(ideal).

(The signification of the let-
ters is fully given in the text.)




FIG. 2. ANOTHER MODIFICATION OP A TYPICAL VERTEBRA.
C, the centrum, giving off d. d. the diapophyses, and r>, 71, the
parapophyses ; the neural arch N, inclosing the spinaTcord, is
formed by n, , the neurapophyses. and n.t. the neural spine;
the hemal arch H, inclosing the great centers of the circu-
lation is formed by ft, ft, the hemapophyses, and hs, the'
hemal spine. From both the neurapophyses and the hema-
pophyses may be given off the zygapophyses, z, z. The lat-
eral arches which may inclose the vertebral arteries O, O,
are completed by the pleurapophyses, pi.



called "hemapophyses;" and by a bone, hs, sometimes bifid, called the "hemal spine."
It also sometimes includes parts or bones called " parapophyses" (Gr. para, transverse).
Bones, moreover, are developed, which diverge as rays from, one or more parts of a
vertebra. Prof. Owen divides the various parts of a vertebra into (1) the autogenous
and (2) the exogenous parts. The autogenous parts arc those which are developed from
independent centers of ossification (q.v.), and are termed the elements of the vertebra;
while the exogenous parts are those that grow from parts previously ossified, and are
termed processes. The line between those two sets of parts cannot be strictly drawn,
since parts which are usually exogenous are sometimes autogenous, nnd rice versa. The
autogenous parts or elements are the centrum, C; the neurapophyses, n,n; the neural
spine, ns; the pleurapophyses, pi, pi; the hemapophyses, h, h, and the hemal spine, /is;
while the exogenous parts or processes are the diapophyses, the parapophyses; the
zygapophyses (Fig. 2), z, z (Gr. zygos, a junction); the anapophvses (Gr. ana, backward);
the metapophyses (Gr. meta, between); the hvpapophysis (Gr. hyjw, below); nud the epa-
pophysis (Fig. 1), e (Gr. epi, upon). These individual parts may be united with each
other in various ways, and may occur in various degrees of development; sometimes
they (or some of them) remain entirely disjointed even in the adult animal, while in
other cases they are united into a single piece, so that their real distinctness can only be
recognized by tracing the history of their development. In most instances some one or
more of these parts will be found to be altogether deficient, while in other cases one set
of parts is exaggerated to a great degree. Thus, in the third or parietal segment of the
human skeleton the neural arch is much expanded, while the hemal one is contracted;
while more commonly, as in the thoracic segment or vertebra of a raven, the hemal
arch is much expanded and the neural one contracted; while sometimes again, as in the
tail of the crocodile and of many other animals, both neural and hemal arches are simul
taneously contracted. The segments are commonly simplified and made smaller as
they approach the end of the vertebral column or axis, one element or process after
another being removed until the vertebra is reduced to its centrum, as in the diagram
of the archetype vertebral skeleton. If we glance at the typical vertebra represented



545



Skeleton.



in Fig. 2, we observe the diapophyses projecting above a canal that serves for the
p.is-a_re of a blood-vessel, and parapophyses which form the lower boundaries of this
canalf Tne.se elements never attain any high development in mammals, birds, or rep-
tiles; thus, in the human cervical vertebra, they form the two roots of the transverse
process surrounding the foramen for the passage of the vertebral artery, while in the

thoracic vertebra of the bird tiie , ....

diapophyses form the transverse
processes, and the parapophyses,
reduced to mere rudiments, form
the articular surfaces with which
the heads of the ribs come in con-
tact. In fishes, however, they are
much developed, and in the cod
tribe are even larger and broader
than the pleurapophyses or true



W

a

o

om
o
a
o




ribs. The ordinary function of
these lateral processes is to afford
attachment to muscles, to protect
the lateral vascular trunks (as in.
the case of the vertebral artery),
and to give support to the pleura-
pophyses, pi, pi, whose develop-
ment varies extremely in different
parts of the same vertebral column,
as well as in different animals.
Then, in the human cervical verte-
bra, they form the short bifid
transverse processes which are an-
chylosed at tlieir base to the
diapophyses and parapopayses,
which surround the vertebral ca-
nal. In the thoracic segments they
are developed separately, and con-
stitute the ribs which form the
greater part of the circumference
of the hetnal arch. Proceeding to
the consideration of the parts be-
low the centrum, we of ten find the
entire henial arch wanting, as in
the cervical and lumbar vertebrae
of man and mammals; but in the
tail of some mammals and of rep-
tile* a heinal arch, protecting the
caudal artery and vein, and closely
resembling a neural arch, is found.
It is in the thoracic region of mam-
mals, birds, and reptiles that we
rind the greatest expansion of the
hernul arch; the hemapophyses
here articulating with the extremi-
ties of the ribs instead of with the
centrum, and the arch surrounding
the entire visceral cavity. In man
and mammals the hemapophyses
remain unossiried, and are known
as the cartilages of the ribs; but in
birds and reptiles they are ossified,
and constitute the sternal ribs.
Thehemal spine, h*, presents great
variety of form, and is often alto-
gether-absent. In the mammalian
thorax it occurs as a flat sternum;

in birds the flatness is replaced by a prominent keel on the mesial line, so that a trans-
verse section almost resembles a neural spine; while in reptiles, again, the henial spine
or sternum is flattened laterally, as in mammals. The hemapophyses and henial spine
are absent in the abdominal region of mammals and birds, but are continued backward
in the saurians or lizard-like reptiles, whose heinal arch is, notwithstanding, incom-
plete, from the absence of pleurapophyses. In serpents the hemal arches are wanting
through the whole trunk, the ends of the ribs being free; and in fishes generally the
hemapophyses and hemal spine are absent or unossified.

Having noticed, as full}' as our space permits, the modifications which the typical
vertebra undergoes in rarious animals, and in different parts of the same animal, we now
U. K. XIII. 85



Skeleton.



546



come to the more difficult subject of "the archetype rertebrate skeleton," which Is
made up of a series of vertebrae arranged in a continuous row. The accompanying
scheme or diagram represents prof. Owen's conception of the common pattern or arche-
type of the vertebrate skeleton. It is difficult at first sight to see any resemblance
between this figure and the human skeleton; but, in fact, the human skeleton, of all
others, recedes the furthest from the common pattern; and if we turn to fishes, which
were the first form of vertebrate life introduced into this planet, we lihd that they
deviate the least from the archetypal idea. If proof be demanded that a given bone in
the human skull is an element of a particular vertebra, it is afforded by tracing the same
bone through its various modifications in mammals, birds, reptiles, and fishes, till the
simple archetypal form is arrived at. The skull is found to be but a continuation of the
backbone, and to consist of four vertebrae or segments, corresponding to the four con-
secutive enlargements of the nervous system, which we call the brain. These segments,
reckoning them from behind forward, are termed the occipital, the parietal, the frontal,
and the nasal segment, Each segment consists of a neural and a hemal arch.

The neural arches are:

N. I. Epencephalic arch (bones Nos. 1, 2. 3, 4 in figure). N. II. Mesencephalic arch
(bones Nos. 5, 6, 7, 8 in figure). N. III. Prosencephalic arch (bones Nos. 9, 10, 11, 12
in figure). N. IV. Uhinencephalic arch (bones .Nos. 13, 14, 15 in figure).

The hemal arches are:

H. I. Scapular ardi (Nos. 50-52). H. II. Hyoidean arch (Nos. 38-43). H. III. Man-
dibular arch (Nos. 28-32). H. IV. Maxillary arch (Nos. 20-22).

The jaws are the modified hemal arches of the first two segments; and the mouth
opens at the interspace between these arches. The position of the vent varies (in fishes),
but always opens behind the pelvic arch, S 62, 63, p, where this is ossified. Outlines of
the chief ossified developments of the denno-skeleton, in different vertebrates, are added
by prof. Owen to the nemo skeletal archetype; as, for example, the median horn, sup-
ported by the nasal spine, 15, in the rhinoceros; the pair of lateral horns developed from
the frontal spine, 11, in most ruminants; the median folds, DI, DII. above the neural
spines, one or more in number, constituting the dorsal fin or fins in fishes and cataceans,
and the dorsal hump or humps in the buflaloes and camels; similar folds are sometimes
developed at the end of the tail, constituting the caudal fin, C, and the anal fin or fins,
A, of fishes.

It has been already remarked that bones which diverge as rays nre formed from one
or more parts of a vertebra. These " diverging appendages" are mainly connected with
the hemal arches, and those which especially concern us are the pectoral apperdagea
of the scapular arch, which become developed into fore-limbs or arms, and the pelvic
appendages which are attached to their supporting hemal arch, 63, ha. If we examine
the skull of a cod-fish, in which the bones have been arranged according lo the segments
or vertebrae to which they belong, we observe that the occipital vertebra has a widely
expanded hemal arch, consisting of three pairs of bones with diverging appendages.
The special names given by Owen to the various elements of that hemal arch, from
above downward, are "suprascapular," No. 50; "scapula," No 51; "coracoid," No.
52. The scapular arch thus formed supports and protects the heart or center of the
hemal system, and in most fishes supports the pectoral fin, while in other animals the
appendage that here becomes a fin is modified into a fore-leg, awing, an arm, and a
hand. Some of the special names originally employed in human anatomy are retained
and applied to like parts in the pectoral fin of the fish; but it will be observed that prof.
Owen designates each bone not only by a name but by a numeral. Of the two flat
bones connecting the fin Avith the coracoid, the upper one is the "ulna," No. 54; the
lower, the "radius," No. 55. the row of short bones joined with these are the "carpals,"
No. 56; beyond which are the metacarpals and phalanges. Ascending from fishes to
reptiles, we find that, in the lower bat rachia (as the omphivma), the scapula are detached
from the occiput, and that other important modifications have occurred. The coracoids
are well expanded, three segments of the diverging appendage are ossified, and two of
these segments are bifid, showing a simple beginning of the radiating multiplication of
parts. The first segment is the seat of these modifications, which have acquired for it
the special name of "humerus;" the two divisions of the next segment of I he appen-
dage are called "ulnar" and " radius;" the gristly mass is the carpus, and the two bony
divisions are the digits or fingers. We have here got so distinct a rudimentary arm,
separated from the head, although, according to the views propounded in this article,
an appendage of the occipital segment of the cranium, that it is unnecessary to trace the
further modifications that ensue, which lead finally to the arm and hand of man. It is
only necessary to remark that in mammals, except amongst the non-placental orders,
the coracoid bone is reduced to a mere rudiment, being known as a process of the scap-
ula, and that its function namely, that of keeping the shoulders apart is performed
by the clavicle, which, according to Owen, is the hemapophysis (58) of the first cervical
vertibra (see fig. 3). With regard to the pelvic arch, we have only space to add that it
must be regarded as the hemal arch of one or more of the pelvic vertebrae; and there is
undoubted evidence to show that the pelvic and scapular arches are constructed on the
same plan; the "ileum" answering to the scapula, the " ischium" to the coracoid, and



547



Skeleton.




Skeleton. K 4 Q

Skew.

the "pubis"to the clavicle; and the same remark applies to the pelvic and scapular
appendages.

"Of this," says Mr. Holden, probably our best authority on human osteology, "a
student may rest assured that, however minutely he may have scrutinized the bones, he
cannot understand them unless he knows something of the 'vertebrate archetype.'
Without this knowledge he is like one who speaks a language fluently, but is igiaoraut
of its grammar. The 'archtype' may be said to be the grammar of all osteo'logy."

SKELETON (an(f). The chemical composition, structure of bone and cartilage, and
their relations, will be found ia the articles BONE, CARTILAGE, OSSIFICATION, and SKELE-
TON, ante. The human skeleton is composed of 200 distinct bones, exclusive of the 33
teeth and the tbree ossicles in each tympanum. See EAR, ante. It is conveniently, and
not unnaturally, divided into four regions: 1. the skull, composed of 23 bones; 2. the
trunk, composed of 54 bones; 3. the upper extremities, composed of 64 bones; and 4.
the lower extremities, composed of 60 bones. In some respects it is more natural to
count 62 bones in the lower extremities, including the hip bones, as they are connected
with the hip joint in much the same m.mner as tue clavicle and shoulder-blade are with
the shoulder joint. These hip bones, however, form a part of a very distinct and func- .
tionally important part of the skeleton, viz., the pelvis, and for this reason it is well to
keep this division of pelvis distinct. See PELVIS, ante. The skull is described under
that title. The trunk may be divided into ribs, 24; vertebrae, 24; and pelvis, 4, the
two lower bones of the spinal, column, viz., the sacrum and coccyx, being included ia
the pelvis. If we include the vertebra and sacrum and coccyx in one division, the spi-
nal column, and the two hip bones with the lower extremities, we shall, in this view,
eliminate the pelvic division. A consideration of the fact that the spinal nerves enter
the sacrum and pass through orifices having the same anatomical relations as the
orifices in the vertebrae, would point to the propriety of placing the vertebrae and
the sacrum and coccyx together, bat tbe physiological connection of these latter bones
with the pelvis present sufficient reasons for the division here made. The trunk has
also 1 sternum, or breast bone, ,and 1 hyoid, or tongue bone (see HYOID BOXE nncl
TONGUE), making in all 54 bones. The ribs are described under tbat title. They are
shown in the cut, 13 on each side; 7 true and 5 false or floating ribs. The true ribs are
joined to the sternum, which is seen to consist of 3 pieces, viz., the manubriura, the
gladiolus, and the eusiform cartilage. The manubrium is the heart-shaped piece to
which the internal ends of the clavicles or collar-bones are joined, their external end
bsing articulated with the shoulder-blade, or scapula, at the shoulder joint, as seen ia
the cut. See CLAVICLE, ante, and SCAPULA, ante. The gladiolus is the middle piece of
the sternum, with which the 7 true ribs articulate. The ensiform cartilage is the small
spatula-shaped piece seen pointing downward into the triangular space between the car-
tilages of the 5 floating or false ribs. The vertebrae are described in the article SPINAL
COLUMN, ante. The pelvis (basin) is seen in the middle of the figure supporting the
vertebral column, and forming with the thigh bones the hip joints. The upper extremity
is divided into bones of the shoulder, 2, clavicle and scapula; of the arm, 1, the hume-
rus (q.v.); of the fore-arm, 2, the radius and the ulna; of the wrist or carpus, 8; of the
metacarpus, 5; and of the phalanges or finger bones, 14 = 32 bones in each upper extrem-
ity, or 64 in both. For a description of the bones of the upper extremity see HAND, ante.
Passing to tbe lower extremities, we observe the femur (q.v.) Its coudyles are seen to
be partly covered in front by the knee-pan or patella (q.v.) Below this are seen the bones
of the leg. The strong bone on the inner side of each leg is the tibia. Its upper expanded
extremity or head forms with the condyles of the femur the knee joint, and.its lower
expanded extremity forms with the astragalus, one of the instep bones, the greater part
of the ankle joint. See LEG, ante, and FOOT, ante. There are 7 bones in each instep, or
tarsus, 5 in the metatarsus, and 14 in the toes, or phalanges, making in all 26 bones in
each foot. These, with the leg, patella, and femur, comprise 30 bones for each lower
extremity, or 6d for both.

SKEL LIGS, TZE, three rocky islands on the west coast of Ireland, about 8 m. west
of Bolus Head, co. Kerry, in long. 1032' west. The lights on the Great Skellig are the
first visible to ships crossing the Atlantic.

SKELTON, JOH.V, an early English satirical poet, is supposed to have been bom about
the year 14GO, but whether in Norfolk or Cumberland is uncertain. He studied at both
Cambridge and Oxford, and received from each the academical honor of laureate. His
sovereign, Henry VII, appointed him tutor to the young prince Henry, afterward king
Henry \ III. ; and Erasmus, in allusion to his learning, styled him the light and grace
of British scholars. A,t this time Skelton had produced some translations, written
elegies on Edward IT. (1483) and the duke of Northumberland (1489). and was author
of some stiff court masques and allegorical poems of little or no merit. He entered
the church in 1498, and became rector of Diss in Norfolk, shortly after \vhich he seems
to have struck into tbat vein of original vernacular poetry, addressed to the multitude,
for which he is unique among our elder bards, and which helped to fix our language.
It consists in a flow of rattling voluble verse, unrestrained satire and jocularity, and a
profusion of grotesque imagery mixed up with Latin and slansr phrases. At times
Sk-elton has gleams of bright fancy and snatches of pleasant description. Of this higher



r, < Q Skeleton.

Skew.

class is his Philip Sparrow, being a poetical lamentation made by a young maiden
(whose charms the poet describes with great gusto and minuteness) over the loss of a pet
bird slain in a convent of black nuns at Carovve near Norwich. The most humorous of
hi* pictures of low life often coarse enough are found in the piece entitled The Tun-
ing [or brewing] of Ely nor Rummy ng, an ale-wife at Leatherhead in Surrey. This poem
was highty popular, and was often reprinted in black-letter, garnished with a rude
wood-cut representation of the fat hostess. His best satires are L'oliit Clout, and Why
Come Ye not to Court? The former is a general satire on the clergy; and the latter, a
virulent attack on cardinal Wolsey, whom the unscrupulous poet had previously flat-
tered, but who had disappointed him of a prebend which he coveted. In this scurrilous
lampoon, "VVoisey is not only charged with arrogance, avarieiousness, and inconti-
nence, but is reminded of his "base original" and "greasy genealogy," having been
" cast out of a butcher's stall." The enraged cardinal ordered his libeler to be arrested,
but Skeltou took refuge in the sanctury at Westminster, and received the protection of
abbot Islip. From this retreat he did not dare to emerge, but continued silent under
its sacred shelter till his death in 1529. The " pithy, pleasaunt, and profitable workes
of maister Skelton, Poete Laureate " were collected and published in 1508, and re-
printed in 1736. An edition, carefully edited by the rev. A. Dyce, was issued in 1843,
in 2 vols. 8vo.

SKEPTICISM (Gr. sktptomai, " I consider ") strictly denotes that condition in which
the mind is before it has arrived at conclusive opinions when it is still in the act of
reflecting, examining, or pondering over subjects of thought. Skepticism is there-
fore the opposite of dogmatism (see DOGMA). The notion of "disbelief" is quite a
secondary meaning of the term. Among the Greeks a skeptikos, "skeptic," was origi-
nally only a thoughtful person, and the verb skeptoinai, never acquired any other signifi-
cation than "to consider." But inasmuch as the mass of men rush to conclusions with
haste, and assert them with far more positiveness than their knowledge warrants, the



Online LibraryFrancis LieberLibrary of universal knowledge. A reprint of the last (1880) Edinburgh and London edition of Chambers' encyclopaedia, with copious additions by American editors (Volume 13) → online text (page 126 of 203)