1. Miriam Claude Meijer, Ph.D. E-C/ASECS Rosemont, PA "Petrus Camper’s Protean Performances: The Metamorphoses“ Camper’s "Two Lessons on the Analogy that exists between the quadrupeds, birds, and fish."

2. 13-14 October, 1778 Camper demonstrates in his first lesson the real analogy that exists between the quadrupeds, and, in his second lesson, how, thanks to this analogy, all animals can be drawn correctly. Having a personal collection of skeletons, he was able to discover that all animals, even fish and birds, are like quadrupeds from comparative anatomy.

3. First General Rule Animals that are not low enough to the ground to scoop up their food are compensated by a long neck. Fish and snakes don't have necks because they don't need necks; they feed directly. The forequarters of animals, whose high legs require a long neck, are always lower than in other animals, i.e. sheep, deer, and camels have back spines and haunches that slant diagonally.

4. Second General Rule The stomach area is much larger among herbivorous animals than among carnivores, and much, much larger among those that chew the cud than animals who aren't ruminants. Intestines do not need as large a volume to convert flesh into flesh as they do to change grass into flesh. The cow eats once to fill his belly and then chews the cud, whereas the horse eats continually. Therefore the cow has a bigger stomach than the horse; the horse than the dog, and etc.

5. Third General Rule Animals are as long as they have number of vertebrae in their loins (the elephant has three, the horse 5, the cow 6, the lion, cat, and camel 7).

6. Fourth General Rule Among animals like the elephant, horse, bull, deer, camel and all ruminants (also the pig), the feet have solid horn or clefts so that they can stand the necessary long time it takes for them to feed themselves. In all the other species, the foot ends in toes. More than 5 is never found among the quadrupeds.

7. Fifth General Rule Among the birds, wings end in fingers too. All have a thumb, most have in addition two fingers, and several species have nails, e.g. the ostrich.

8. Plate III, Figure 1 - The Horse

9. Petrus Camper As the most beautiful quadruped and the most useful animal to man, the horse makes a good prototype. Let BCDEF be the body and the legs of a horse in such a manner, that the legs, in order to be good for racing, be as high as GE and HD. Draw the line AI (the purple line) to represent the direction of the vertebrae. The line AY (green line) is the first rib, and, as a result, "A" (green circle) is the center of movement of the first vertebral in the neck (all animals have 7). The neck and the head together must be long enough so that the animal can eat, i.e. AY (green line) + YZ (blue line).

10. The Horse When the head is smaller in relation to the height of the animal, the neck must be able to stretch all the more, as is the case in camels, sheep, etc. When the head lifts, the neck must curve either on the outside (the outer brown line) or on the inside (the inner brown line) as in old horses.

11. The Horse In order to have such a neck, the spine protuberances of the vertebras in the back have to be able to lift a lot; and they do in the horse (in AB). The length of the protuberances are less considerable in the other animals; particularly less so in man, who carries his head in a straight line. The horse has a big muscle (the red line) which is the reason horses can kick (an unique characteristic of the species). The cow does not have this muscle and is therefore characterized by a hollow in that same area (blue patch).

12. Plate III, Figure 2 - The Cow

13. The Cow The outline of the horse is sketched again (in red) and the feet of the horse has to shorten into those of the cow. From this result that the neck does not have to be as long: only as AF (brown line) when raised and as AY (green line) when grazing. The neck does not need to shorten therefore, like in the horse, but raises in a diagonal direction that the head remains always lower, because of its weight and its horns, than the withers at point "B" (red circle), which for that reason is not as high as in the horse.

14. Plate IV, Figure 3 - The Dog

15. The Dog The outline of the horse (in red) and the line that passes through the vertebras (purple) is traced again. Because of the change in food, change the horse stomach outline into the "green line." The neck can be of different lengths because the dog eats while lying down or launches without needing to graze the muzzle on the ground. Its paw, in order to be lighter, have to be skinnier. The bone of the leg being longer, the "brown line" becomes much shorter than in the horse. The tail must serve in the movement of jumping.

16. Plate IV, Figure 4 - The Camel

17. The Camel Stretch the feet, enlarge the stomach, the neck becomes proportionally longer; the head of this animal stays as large as the horse's even though it appears smaller because of the other differences. It has to have a curved neck because of the center of gravity. In the camel, sheep, and deer, the line AT (purple) has to be in a diagonally lifting angle.

18. Plate V, Figure 5 - The Elephant

19. END OF FIRST LESSON If you gave the neck a length of AF (the brown line), you would need a high withers, but, because of the weight which must be supported due to the structure of the animal, this kind of neck cannot be. The neck must be very short: "green line." The animal, not being able to reach the ground, requires thus a trunk. There is all the more evidence in the case of the walrus. It does not need a trunk because it swims for food. The vertebras of the chest and back must form an arch. Having only 3 vertebras in the loins, this animal seems shorter in our eyes.

20. SECOND LESSON These facts of anatomy can be applied to art. Except for Chrispyn van de Pas, no one has ever given particular rules to draw all the animals with any kind of real precision. The skeletons—which in animals like in man furnish the real base of their exterior appearance—are so poorly represented and so erroneously treated that it is impossible for painters to get the least use from them.

21. Chrispyn van de Pas In his Ouvrage, Part V, page 6, Van de Pas gave an easy method to sketch a horse or cow without ruler or compass:

22. Chrispyn van de Pas According to him, one should draw a square, divide it into 9 equal parts and draw 3 circles: one for the shoulders and chest; a 2nd for the belly; and the 3rd circle for the rump. However, everything in van de Pas's method is either ultimately based on conjecture or is actually physically incorrect. Nor is it possible to draw the animals in a different perspective.

23. Chrispyn van de Pas

24. Plate V, Figure 8 - Back to the Horse

25. Four Drawing Rules Trace ABC (the purple line) according to the direction it must have, i.e. according to the characteristic of the animal that must be represented, either in a horizontal angle or in a more diagonal one towards "C" such as would be required in the sheep or camel. Complete the sloping circle to "D" (dotted purple line). Draw FE (green line on the left) for the bone of the shoulder-plate and CH (green line on the right) for the bone of the hip which is equal to 2/3 of the head for the horse but equal to the head itself in the cow.

26. First Drawing Rule Sketch the bone of the arm EG (dotted green line on the left) and the bone of the thigh IK (dotted green line on the right) so that the elbow and the knee in the horse, cow, etc. are of equal height and in the same alignment with the stomach. Complete the contour of the front and hind legs, i.e. trace out KL, MN, NO for the back and GR, RS, ST for the front (all blue lines). When "R" and "L" (blue circles) are of equal length, the "heel" ML (red line) is naturally raised. Outline the neck, according to the particular characteristic of the animal, and then the head. This fundamental outline—with Camper's general rules from the first lesson—can be applied to all kinds of animals.

27. Second Drawing Rule To get the shapes of the front and back legs, add the muscles at "Q" (the brown circle) to the arm bone and the rest of the muscles (brown dotted lines) in the front and back.

28. Third Drawing Rule The first ribs are always straight and covered by the shoulder blade. Those in the back are always placed diagonally backward. In the horse they extend until the hip bone, but in the cow, as that part of the loins is longer, a triangular cavity or hollow is formed (blue shading in Figure 2).

29. Fourth Drawing Rule In all the animals with sole or clefts, the hand and foot are very long, like in RS and MN (dotted red lines). In the animals which leap, like lions, dogs, rabbits, the bone of the leg is very long but the foot very short.

30. Plate VI, Figure 9 - Application of these Rules to Birds

31. The Bird Trace a new oval. Situate the arms in AB (purple line) which, if the bird does not fly, must be folded as in BC (dotted purple line). Take CD for the hand, DF for the thumb, and DE for the other fingers. Then trace GH (green line) for the bones of the hip and the rump. The red line (IK) gives you the thigh KL (red dotted line) the bone of the leg under it, the feet, and the toes.

32. The Bird Trace the neck observing its proportion to the height of the body and culminate the head. In some species the upper jawbone is very mobile, e.g. the eagle, parrot, and duck. When the bird is of a species that flies, it must have a bony eminence in the form of a ridge on the breast bone in order to insert muscles. Birds that do not fly, like the ostrich, do not have this crest. Add muscles and feathers to complete the animal.

33. Note Having proved that the front feet of all quadrupeds and the birds are analogous to our arms, it follows that it is absolutely absurd to give wings to the human figure, as the custom has held for angels and cupids.

34. Plate VI, Figure 11 Proof that Fish are analogous to Quadrupeds in terms of their Interior Structure

35. The Fish Begin again with the form of the trunk BACG (purple line).

36. Seeing that the fish does not need a neck at all and therefore hardly has one (except for those that breathe which have a slight neck), the head is attached directly to the spine of the back at point "A" (red circle). In this state the fish cannot make a single movement, as he is in equilibrium with the water, so it is necessary to give it a motor force in the form of an oar like in a boat (green line on the left) with which the fish can be compared. But because this motor force must of necessity reside in the fish itself, the tail CH (brown line) and the transversal suspensions of the vertebrae, to insert its muscles, are indispensible. The longer the tail, the faster the fish can swim.

37. NOTE I It has been established that a boat has the least mobility possible than the center of motion and of gravity meet at the same point. This is not possible in a boat, but always takes place in the fish; the latter therefore has the ability to swim in a straight line whereas boats can only advance by making movements from side to side with the prow. But, as the fish needs to keep itself upright, it has fins at the chest (BF) and on the stomach at point "G" (green lines on the right). If one cuts the fins BF, as did Actedi, the fish cannot support itself and rolls upside down.

38. NOTE II The center of motion must vary in ratio to the weight of the fish's head and from that also must depend the length of the tail. From this, therefore, the forms of fish are the most susceptible of being diversified and they have more varieties than among the quadrupeds. Linnaeus counted 212 species of quadrupeds to the 480 among the fish. It is also obvious that it would be ridiculous to believe in the existence of mermaids. Finally, seeing that fish advance by tail movements, explains why they do not need feet, thighs, leg bones, etc.

39. Plate VI, Figure 10 Nature gives us the most admirable and spectacular example of what has been advanced here in the metamorphosis that takes place in the frog.

40. Plate VII, Figure 12 - Cow into a Bird

41. Cow into Bird In erecting only the trunk in the manner of GC (purple line), it follows that the front feet lift off the ground and that, as the center of gravity is no longer supported by the front, it must be by the back feet in EI (blue line). The trunk "G" (red circle) raising considerably from the ground, the neck must be stretched in GH (red line), and the head must be carried towards the back to coincide with the line of propensity in HI (dotted red line). The front feet, rendered unfit for walking, are thus wings and terminate in accordance to Camper's general rules.

42. NOTE Birds, being covered in feathers, are not tormented by flies, and hence do not require a long and flexible tail as among the quadrupeds.

43. Plate VII, Figure 13

44. Quadruped into a Human As the multiplicity of lines produces too much confusion, it is better to draw, for example, a horse on 4 legs and demonstrate on those of behind how the hips meet at a single point (green line).

45. that the hips will be compressed into a right line with the hams or thighs; that the front legs coming to hang along the body in the manner of arms require as a result the necessity to be supported by the collarbones; that the thighs and the legs find themselves necessarily in a one and same straight line; that the head does not need to be at the end of a long neck and therefore needs no high withers;

46. that the back becomes flat; that the head, having the brain and the cerebellum placed one in front of the other in a horizontal line, is now closer to a spherical shape and the center of gravity and of movement must meet at a single point; that it is of all necessity that the jaw retreats inside, and, as a result, that the nose yields to the outside; that the feet are curtailed; and that 5 toes have to be given to the feet.

47. NOTE It follows from the 3rd rule that the thighs, the calves in man and even the buttocks, have to be more fleshy, in proportion, because of the need of the trunk to keep itself upright. (Aristotle had noticed that only man was tailless and had buttocks, and concluded that it had to be due to the fact that he was the only animal that stood.