Internalism and Laws of Form 319
formed the pectoral girdle. He kept Oken's names—parietal, frontal, and nasal—
for neural halves of the three anterior vertebrae, and designated the haemal
(ventral) halves by their associated structures: hyoid, mandibular, and maxillary.
Having thus resolved one of the two problematic bone groups by traditional
arguments, Owen turned to the single remaining issue for completion of the
archetypal research program—the explanation of limbs and associated girdles as
modified vertebral parts. In this sense, The Nature of Limbs should not be read as a
specialized treatise on one part of the body, but as an attempt to complete the most
radical version of formalism by bringing the last outpost of the vertebrate skeleton
under the vertebral archetype.
Owen's argument for limbs might strike us today as contrived and peculiar.
His effort does not represent the high water mark of formalist logic even in its own
terms and times, but may still win our grudging respect for ingenious-ness and
pure chutzpah. The apparent problem, after all, can only be described as daunting.
After using all the lateral and ventral parts of a vertebra to build the girdle, what
remains for constructing the prominent complexity of humerus, radius and ulna,
carpals and metacarpals, right down to the most distal phalanx of the digits? Surely
these bones can only be "novel" structures unrelated to the archetypal vertebra, and
the integrative program of archetypal reduction and genesis must fail. We might
choose to downplay the supernumerary status of a stapes or hyoid bone; but we can
scarcely disregard the need to encompass limbs within any general theory of the
vertebrate skeleton—for an archetype that omits such a major structure can only
provide a partial and paltry explanation indeed.
Owen's improbable solution homologizes the vertebrate limb, in all its
complexity, with a simple, unbranched projection from the haemapophysis (see
Fig. 4-13), called a diverging ray (note the ray on each vertebra of the archetype in
Fig. 4-14).
But how could Owen justify a comparison of so many articulated bones with
a hypothetical single rod? Owen used the time-honored comparative method by
attempting to trace back the complexity of vertebrate limbs in a structural series of
simplification, leading to the lungfish Lepidosiren and its minimal pectoral ray.
Lest this series be rejected as a concatenation of heterogeneous objects, Owen
presented a tripartite argument: (1) the structural series denotes a descent by
simplification; (2) simplification occurs by "arrest of development," bringing the
reduced form closer to an embryonic state; (3) the embryo, following von Baer's
principles, reveals the generating archetype in a way that the complexly modified
adult cannot. Sensing that opponents might view the proposition as a
"transcendental dream," Owen defended his structural series (Fig. 4-15) as a
voyage to the archetype: "It is no mere transcendental dream, but true knowledge
and legitimate fruit of inductive research, that clear insight into the essential nature
of the organ, which is acquired by tracing it step by step from the unbranched
pectoral ray of the lepidosiren to the equally small and slender but bifid pectoral
ray of the amphiuma, thence to the similar but trifid ray of the proteus and through
the