692 
PROFESSOR WILLIAMSON ON THE STRUCTURE AND 
fissures in the vertical section are still more strongly defined than in those examples. 
They are however filled up in the same way as in the Plaice, by transverse laminae of 
inembraniforiu bone. If the osseous neurapophyses have ever been independent of 
the centrum, they have become united at an exceedingly early age, since many of the 
lamellae which enter into their composition may be readily traced down into the 
interior of the centrum. 
On making a vertical section through the vertebra of the Cod {Morrhua vulgaris, 
Cuv.), parallel with the spinal axis, we see very clearly that the growth of the two 
terminating articular cones, and that of the laminae by which they are connected 
together, have proceeded consentaneously. The osseous substance of these cones 
forms two thick and well-defined margins in a section so prepared. At the first 
glance, each of these terminal tissues appears to have been formed by the addition of 
new laminae to their external or articular surfaces. This appearance however is fal- 
lacious, and arises from the existence of a series of minute radiating nutrient tubes, 
which permeate this portion of the bone at right angles to the real lines of growth ; 
in the vertico-longitudinal section the latter are really transverse, and parallel with 
its peripheral surfaces. Nothing is easier than to show that the lamellee, of which 
the longitudinal plates consist, are also prolonged into these marginal cones, and that 
the latter have been developed entirely by the successive additions of concentric 
lamellse to their peripheries. The whole vertebra thus resembles a succession of thin 
closely-fitted cylinders, placed one within another, each one being successively larger 
than that which it invests ; only instead of these cylinders being entire throughout 
their whole length, they are so only at their two extremities; the intervening portions 
being alike flexed and excavated, so as to produce the less regular laminse forming 
the cancelli occupying the interior of the vertebra. The edges of the cylinders thus 
superimposed constitute the concentric rings seen in the concave articular extre- 
mities of each of these bones. 
I am unable to see how this structure and mode of growth can be reconciled with 
the idea of the terminal cones being separately developed from two independent 
osseous centres, as thought by Professor Owen*. Corresponding sections of the 
vertebrae of the Pike, Plaice, Haddock, Perch and other fish, all lead me to correspond- 
ing conclusions as to the way in which these portions of the bones have been formed, 
though none of my sections show it with the same degree of clearness as those of 
the Cod. The small nutrient tubes in the latter example have been formed in the 
same way as the Haversian canals in the other bones of the Pike, by the omission of 
apposite points from the substance of the successively added lamellae, which, as 
already observed, these tubes penetrate at right angles to their plane. 
I am well aware that these views respecting the development of many vertebrae 
and their apophyses from one common centre of ossification, will not escape opposi- 
tion, controverting as they do the ideas of some of our most justly distinguished 
* On the Archetype and Homologies of the Vertebrate Skeleton, p. 82. 
