(1) Sense Organs
(2) Common Integument.
The term =topographic anatomy= designates the methods by which the
relative positions of the various parts of the body are accurately
determined. It presupposes a fair working knowledge of systematic
anatomy.
=Descriptive Terms.=—In order to indicate precisely the position and
direction of parts of the body, certain descriptive terms are employed,
and must be understood at the outset. In the explanation of these terms
it is assumed here that they apply to a quadruped such as the horse in
the ordinary standing position. The surface directed toward the plane of
support (the ground) is termed =inferior= or =ventral=, and the opposite
surface is =superior= or =dorsal=; the relations of parts in this
direction are named accordingly. The longitudinal =median plane= divides
the body into similar halves. A structure or surface which is nearer
than another to the median plane is =internal= or =medial= to it, and an
object or surface which is further than another from the median plane is
=external= or =lateral= to it. Planes parallel to the median plane are
=sagittal=. =Transverse= or =segmental= planes cut the long axis of the
body perpendicular to the median plane, or an organ or limb at right
angles to its long axis. A =frontal= plane is perpendicular to the
median and transverse planes. The head end of the body is termed
=anterior=, =cephalic=, or =cranial=; and the tail end =posterior= or
=caudal=; relations of structures with regard to the longitudinal axis
of the body are designated accordingly. Certain terms are used in a
special sense as applied to the limbs. =Proximal= and =distal= express
relative distances of parts from the axis of the body. The anterior face
of the thoracic limb from the elbow downward is also termed =dorsal=,
and the opposite face =volar=. In the corresponding part of the pelvic
limb the terms are =dorsal= and =plantar= respectively. In the same
regions =radial= and =ulnar= (thoracic limb), =tibial= and =fibular=
(pelvic limb), may be used to designate that side of the extremity on
which the corresponding bone is situated; they are therefore equivalent
respectively to internal or medial and external or lateral in the
animals with which we are concerned.
It is evidently advantageous to employ terms which are as far as
possible independent of the position of the body in space and capable
of general application, _e. g._, dorsal, ventral, proximal, etc. It is
also desirable that the terms internal and external be reserved to
indicate relations of depth in cavities or organs, and medial and
lateral to designate relations to the median plane. Such terms are
coming into more extensive use in human and veterinary anatomy, but
the older nomenclature is very firmly established and cannot well be
discarded at once and entirely.