Baron Georges Cuvier, and others before him, observed that related groups of organisms (such as vertebrates) have the same basic architecture. For example, in the forelimbs of vertebrates:

• One bone in the upper arm
• Two bones in the forearm
• A bunch of little bones in the wrist
• Long bones in the palm of the hand
  
• Smaller long bones down each finger

• So the wing of a bird, the wing of a bat, the arm of a human, the forelimb of Brachiosaurus, and the flipper of a dolphin are all homologous
• The spike of the hand of Iguanodon and the thumb of humans are homologous
• Homologies represent the same unit of the anatomy, regardless of function

Cuvier, Owen, and other comparative anatomists recognized a second type of similarity: analogous structures:

• Analogies represent different units of anatomy serving the same function
• The grasping finger of Iguanodon is homologous with the human pinky, but analogous to the grasping human thumb

Comparative anatomy seeks to describe the structure of the bodies of organisms in terms of their homologous structures.

Like geography and sailing, there are a set of directions which are useful for indicating different directions. As in geography and sailing, these units come in pairs. Unlike geography, but like sailing, these directions are internal: they are based on the properties within the organism, and not the outside world.

In geography, we have North/South, East/West, Up/Down; In sailing there is Fore/Aft, Port/Starboard. In comparative anatomy, there is:

• Anterior (towards the tip of the snout)/Posterior (towards the tip of the tail)
• Dorsal (up and out through the spine)/Ventral (down and out through the belly)
• Medial (towards the middle)/Lateral (towards the sides)
• Proximal (towards the trunk)/Distal (away from the trunk)
  • Proximal and distal are normally used only for the limbs, and occasionally for the tail

Anatomical directions, like geographic directions, are relative. A bone or landmark can be anterior to something, but posterior to something else:

E.g. The eyes of a typical animal are anterior to the ears, but posterior to the snout
Or, the lungs are generally lateral to the heart, but medial to the ribs

Anatomical views: when a specimen is illustrated, the anatomical view represents that surface of the specimen that is shown:

• If you see the top surface of a skeleton, bone, etc., it is in dorsal view
• If you see the front surface of a skeleton, bone, etc., it is in anterior view
• If you see the outside surface of a skeleton, bone, etc., it is in left lateral or right lateral view (depending if you see the left or right side, respectively)
• And so on...

Anatomical landmarks: particular structures on the skeleton (openings, joints, etc.) used for identifying the position of bones or other features of the anatomy. Like geographical landmarks, they are generally easy to recognize.

The skeleton of a dinosaur (or other vertebrate) is divided into a couple of different sections:

• The skull, composed of:
  • The cranium (braincase, face, and upper jaw)
  • The mandible (lower jaw)
• The postcranium (everything posterior to the cranium), composed of:
  • The axial skeleton (spine, ribs, and related features of the neck, trunk, and tail)
  • The appendicular skeleton (forelimb, hindlimb, and their girdles)

(Incidentally, anatomical terms are for the most part based on Latin words. Bones or landmarks with Latin rather than English plurals are noted below)

Bones and Landmarks of the Skull
NOTE: Almost all bones and landmarks of the skull are paired, with one on the right side and one on the left. Although the skulls of vertebrates are composed of many bones, these bones are joined by sutures: depending on the type of suture, the joint can be mobile or immobile.