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ANATOMY.
Special
Anatomv.
PART I.
ANATOMY OF THE ORGANS OF THE ANIMAL, VOLUNTARY,
OR RELATIVE FUNCTIONS.
The organs belonging to the functions of animal life
are those of locomotion, sensation, voice, and innervation.
1 ese organs are distinguished by two general characters,
symmetry of form and harmony of action. By the first
!s meant that each organ possesses similar parts on each
side of the mesial plane. By the second is meant that
the action of that part which is on the right side of the
mesial plane corresponds with that on the left.
CHAP. I. THE ORGANS OF LOCOMOTION.
The organs of locomotion may be arranged in two orders,
active and passive. The first are the agents of motion,
or the organic substances which produce motion; the se¬
cond are the bodies moved, or the instruments of motion.
The muscles, strictly speaking, are the former, though to
these are added certain appendages. The bones and their
appendages constitute the second.
With the latter order of parts it is usual to begin the
business of special anatomy, for obvious reasons. The
bones are at once the most durable and regular in shape
of all the organic solids; and as an intimate relation sub¬
sists between their mechanical figure and the soft parts
connected with them, the knowledge of the former con¬
stitutes the best introduction to that of the latter species
of organs.
SECT. I. OSTEOLOGY, SKELETOLOGY.
The assemblage of bones composing the human body
constitutes the skeleton, which, like the body, is divided
into head, trunk, and extremities. The length of the
skeleton is about an inch less than that of the body; that
is, the skeleton of an individual 5 feet 8 inches in height is
about 5 feet 7 inches long, and of one 6 feet, about 5 feet
11 inches long. The weight of the skeleton varies at dif¬
ferent periods of life. That of a middle-sized adult ranges
between 160 and 200 ounces. A male skeleton, measur¬
ing 5 feet 6 inches long, I found to weigh 168 ounces,
or 101 ]bs>j avoirdupois.
The number of separate pieces amounts to 254, of which
56 belong to the trunk, 60 to the head, 72 to the pecto¬
ral extremities, and 66 to the pelvic. Of these several
parts, the trunk is the most important, because, Is#, it is
developed before the head or extremities; and, 2dly, be¬
cause if we look to its place in the animal kingdom ge¬
nerally, it is the most essential and constant, and pre¬
sents the general modulus or type according to which the
osseous pieces composing the head are constructed.
The Trunk.
The trunk. The trunk of the skeleton consists of three parts, the
spine or vertebral column, the chest or thorax, and the
pelvis.
§. 1. The Spinal or Vertebral Column.
Vertebra!.)
(Spina Dor si;
wJer' '^ie ver*:e^)ra^ column, situate in the posterior part of
Jumn. C°" I"jrunk’ length of which it determines, unites the
head to the pelvis, supports the former, and is supported
by the latter. When completely developed, it consists of
29, and rarely of 30 pieces, named vertebrae (spondyli,
tf^ovSuXo/), from the circumstance that each admits of a
slight degree of rotatory motion. .Twenty-four of these
bones, which are in the healthy adult separate, are de- Special
nominated true vertebrae (vertebra: verve). The 25th, Anatomy
named the sacrum, though in adult life forming a single
bone, consists in early life of four separate pieces, which ver^
become consolidated, and are therefore named false ver- brae
tebrev, (vertebra: spuria:). The four last constitute what is
named the coccyx, dhe column thus formed, though
straight at birth, assumes afterwards several curvatures
in the antero-posterior direction, giving it the aspect of
the Italian f. It may be divided into four regions, the
cervical, dorsal, lumbar, and sacral. In the first it is al¬
most straight, but begins to bend backward in the second,
so as to form a considerable curvature with the convex
surface posteriorly. A little below the middle of the
dorsal portion it bends forward, and continues to do so to
the lower part of the lumbar region, where it once more
bends backward, and forms the sacrum into a concave
hollow. At the lower end of the sacrum it again in¬
clines forward, and the coccyx is in general considerably
incurvated anteriorly. (Plate XXVI. fig. 1.)
Besides the antero-posterior curvatures, there is in ge¬
neral a lateral one near the lower part of the dorsal re¬
gion, on the left side, to which its concavity is directed.
This has been observed by anatomists, from Cheselden,
who first represented it, to Soemmering, Bichat, and
Meckel.
In length the vertebral column does not vary much ;
and differences in stature depend more on the dimensions
of the members than of it. In thickness it augments
progressively from the cervical to the sacral portions, af¬
ter which it once more tapers to a point. It may be com¬
pared to two cones united by their base, the superior of
which is truncated.
The vertebrae, true and false, possess certain common
characters. . Of these the most general is the annular
shape, or a ring of bone, the opening of which, in conti¬
nuity with those of the whole column, constitutes a lon¬
gitudinal cylindrical cavity for lodging the spinal chord
and its envelopes. It is therefore denominated the hole
of the spinal marrow (foramen medulla: spinalis, Soem.),
or simply the vertebral hole (Bichat). Anterior to this is
a mass of bone, generally the largest of the vertebra, and
therefore named its body (corpus vertebrae). The ante¬
rior surface is flat, sometimes slightly convex; the poste¬
rior is always concave; the upper and lower surfaces are
slightly concave, and correspond with the intervertebral
fibro-cartilages.
Behind the hole the vertebra is moulded into an arch
or annular segment, the outer surface of which forms
seven processes. The first at the back of the vertebra
on the median line is the spinous process, which may be
said to be formed by the union of the spinal plates in the
middle. On each side are two, which, from their situation
with respect to the column, are named transverse pro¬
cesses. Other four, two on the upper and two on the
lower surface of each vertebra, near the base of each
transverse process, are named oblique, from their direction,
and articular (processus articulares), because the inferior
ones of the superior vertebra are articulated with the su¬
perior ones of the lower vertebra. These processes are
easily distinguished by being covered with cartilage and
synovial membrane. They constitute true capsular joints.
Each vertebra presents four notches or depressions,
two at the upper and two at the lower surface, between
the body and the oblique processes. Each of these, with
coiresponding notches on the vertebra above and below,
forms a hole (foramen conjunctionis, vel intervertebrale),
for the exit of the spinal nerves and the entrance of
blood-vessels.