CHAPTER I. General Considerations of the Animal Form

Dorsal

The back or upper side (posterior in human anatomy)

Ventral

the under side (anterior in human anatomy)

Lateral/Medial

the sides, right, and left/ towards the midline

**Anterior, Cephalic, or Cranial**

the head end of the animal (superior in human anatomy)

**Posterior or Caudal**

the tail end of the animal (inferior in human anatomy)

Median

the middle

Central

the part of a system nearest the middle of the animal

Peripheral

the part nearest the surface

Proximal

nearest the origin, near the main mass of the body, as the thigh

Distal

further away from the origin, away from the main mass of the body, as the toes

Superficial

on or near the surface

Deep

some distance below the surface

Superior

on or near the surface

Deep

some distance below the surface

Superior

above/head

Inferior

below/feet

Median plane

 It divides the body into two **nearly identical halves, right and left.**

Sagittal plane

**right and left, not identical**

Horizontal or Frontal

front/back

Transverse or Cross

upper/lower portion

Longitudinal or Antero/Posterior Axes

line in the median sagittal plane extending from head to tail

Sagittal or dorsoventral axes

any line in the median sagittal plane extending from dorsal to ventral surfaces

Transverse or Mediolateral

any line in the transverse plane running from side to side

Spherical

type of symmetry where there’s finite number of symmetry (round)

Radial

**actinomorphic**; laid out equally from a central axis (flattened) symmetry

Bilateral

only the midsagittal plane divides; single/simple symmetry

Metamerism/Segmentation

regular repetition of body parts along the anteroposterior axis.

Homonomous

segmentation of the animal body into nearly like segments

Heteronomous

various segments differ from each other to a greater or less extent

Cephalization

tendency of the anterior body to become distinctly differentiated from the body

Homologous structures

those which, however unlike in function or superficial appearance, have the same origin, as demonstrated by the study of their embryonic origin and development and their paleontological history. 

Analogous structures

resemble each other either in superficial appearance or in function but have had different origins.