Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

42 ANATOMY.
Special of the former readily explains the difficulty of maintaining
Anatomy, attitude for a long time.
Progression or gait (incessus) consists in the anterior
sion^68" propulsion of the person by the alternate propulsion of
each pelvic extremity. In this, therefore, not only are
the muscles necessary to maintain the erect position put
in action, but those which bend the lower extremity on
the trunk operate on one side, while the extensors of the
other maintain that extremity for the instant fixed. Pro¬
gression consists of a series of steps (passus); and each
step consists in the antero-posterior separation of the pel¬
vic extremities by the propulsion of one, while the other
remains fixed. Supposing the left foot to be the fixed
one, the right foot is elevated, and the leg is propelled by
the contraction of the gemellus, solceus, semitendinosus,
tibialis anticus et posticus ; while at the same time the ex¬
tensors of the knee raise the leg, and the psoas, iliacus,
pectinceus, triceps adductor, sartorius and gracilis, with
the tensor vaginae femoris, raise and stretch the whole
limb. When this is accomplished, the right foot, with the
knee extended, the elevating muscles being relaxed, and
the trunk, are inclined forwards, and the foot is planted at
some distance before the left.
In this motion, however, in which the trunk is carried
forward by the recti and obliqui abdominis, and downward
by the psoae and iliaci interni, and the leg by the long
flexor and the anterior peronceus, a fall would be the im¬
mediate result, unless the knee, to preserve equilibrium,
were somewhat bent, and the other foot at the same time
began to assume the same action. While the toes, there¬
fore, are forcibly impelled by their flexors to the ground,
the two gastrocnemii, the anterior and posterior tibiales,
and the peroncei, elevate the foot with the sole backward,
and bend the knee, and the psoas and iliacus raise and
extend the whole member.
Running. Running differs from progression, not only in velocity,
but in the mode of its accomplishment. Not only are the
pelvic extremities more inflected and moved than in
mere walking, but they remain inflected. Thus, while
the trunk is inclined forward on the pelvic extremities
by the recti cruris, the psoae and iliaci, the two latter
with the pectinceus longus, the adductor longus and brevis,
and the tensor, are employed to inflect the thigh, the semi¬
tendinosus, semimembranosus, and biceps to inflect the leg,
and the anterior tibialis, great and small extensors of the
toes, and extensor of the great toe, are employed to bend
the foot and the phalanges on the metatarsal bones. The
last action is essential to running, which is always most
perfect on the tip of the foot. In this movement also the
centre of gravity is constantly undergoing change, and is
not only carried forward, but makes a sort of undulating
motion on each side, and above and below the plane of
motion. This is the effect of the pectoral extremities
being employed to balance the person.
Leaping. In leaping, the pelvic extremities are much inflected,
and the sole of the foot rendered tense, by the gastrocne¬
mius, solceus, tibiales, and. peroncei, while the extensors are
employed to raise the phalangeal part of the foot; when
the person is forcibly impelled forward by the gastrocne¬
mius, solaeus, the leg suddenly contracting on the crurceus
in the thigh, and the glutceus, semitendinosus, semimem¬
branosus, and biceps in the pelvis.
Dancing. In dancing, the muscles are made to co-operate in pro¬
ducing a number of complicated motions. In most of the
motions composing the dances practised in ordinary socie¬
ty, while the muscles of the pectoral extremities are em¬
ployed in balancing the person, and those of the trunk in
maintaining it in the erect attitude, the flexors and ex¬
tensors are employed to diduct, inflect, or extend; to
cross the extremities with more or less rapidity ; and, Special
while the extensors and tibialis anticus elevate the person Anatomy,
on tip-toe, the lateral peroncei are employed to evert the
foot and point the toes.
CHAP. II.—THE ORGANS OF SENSATION.
The organs of sensation may be distinguished into two
orders, according as their province is to recognise general or
peculiar affections and qualities in external objects. Thus,
while it is the purpose of touch to recognise the consis¬
tency, shape, and resistance of bodies, it communicates
no information regarding their colour, smell, or taste, or
the effects which their collision produces in the vibra¬
tions of the atmosphere. With these affections of the ma¬
terial world man becomes acquainted by means of organs
of a peculiar construction, and adapted to receive the
impressions occasioned by these qualities. These organs
are, for smell, the nostrils and their appendages; for colour
and the general purposes of sight, the eye; for taste, the
palate and mouth; and for sound, the ear. For the pur¬
poses of common sensation the skin is the agent; but on
the structure of this membrane it is unnecessary to add any
thing to what has been already said in the General Ana¬
tomy, unless that in certain regions, for instance the tips
of the fingers, the erectile arrangement of the capillaries,
with a minute distribution of nerves, and great thinness
of cuticle, communicates the delicacy necessary to the re¬
fined purposes of tact.
SECT. I. THE ORGAN OF SMELL ; THE NASAL CAVITIES.
The organ of smell consists of an external part for re¬
ceiving and transmitting substances capable ot producing
the sensation of smell; and an internal part, in which this
sensation takes place.
The nose (nasus), which constitutes the external part, The nose,
is a pyramidal eminence, bounded above by the forehead,
below by the upper lip, and on the sides by the orbits and
cheeks. It has two anterior-inferior oval-shaped lateral
openings named the nostrils (nares), separated by a par¬
tition. ^ It consists above of the nasal bones and the nasal
processes of the superior maxillary bones, covered by
periosteum, cellular tissue, part of the compressor narium,
and skin. Below, it consists of membranous fibro-carti-
lages, attached to the nasal bone and superior maxillary
above and behind, and supported by a middle cartilage
{septum narium), which rests on the fissure of the vomer
below, and is fixed to the vertical plate of the ethmoid
bone above, and to which is attached a slip of fibro-
cartilage before, named columna nasi. The lateral fibro-
cartilages, which are occasionally named wings {alee nasi,
pinnae nasi), covered by cellular tissue, muscles, and
skin, liberally supplied by blood-vessels and sebaceous
follicles, are moved by the levator, compressor, and two de¬
pressors. These parts, with the middle septum and co¬
lumna, are lined by a form of mucous membrane named
the pituitary or Schneiderian.
To what was already said of the nasal cavities under
the head of Osteology it is superfluous to add any thing,
unless what relates to the lining membrane, the distribu¬
tion of which is exactly according to the extent of the
bony walls of these cavities and their subdivisions.
This membrane consists of two layers; a fibrous, which is Narine
the periosteum or perichondrium of the nasal cavities; and membrane,
a mucous, resembling the other forms of this tissue. It
is soft, spongy, red, and more or less vascular, with an at¬
tached and a free surface, the latter secreting the thin
mucus necessary to preserve the membrane in a proper
state for receiving odorous impressions. In this mem-
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