432 



and in that case there would be five neurapophyses to three central 

 and three neural spines. Furthermore, it is precisely to these two 

 superfluous elements that the only two clear and obvious hsemal 

 arches, the mandibular and hyoid, are attached. 



I confess I do not perceive how it is possible, fairly and consistently, 

 to reconcile these facts with any existing theory of the vertebrate 

 composition of the skull, except by drawing ad libitum upon the Deus 

 ex machind of the speculator, imaginary "confluences," " conna- 

 tions," "irrelative repetitions," and shiftings of position by whose 

 skilful application it would not be difficult to devise half a dozen 

 very pretty vertebral theories, all equally true, in the course of a 

 summer's day. 



Those who, like myself, are unable to see the propriety and ad- 

 vantage of introducing into science any ideal conception, which is 

 other than the simplest possible generalized expression of observed 

 facts, and who view with extreme aversion, any attempt to introduce 

 the phraseology and mode of thought of an obsolete and scholastic 

 realism into biology, will, I think, agree with me, not only in the 

 negative conclusion, that the doctrine of the vertebral composition 

 of the skull is not proven, but in the positive belief, that the relation 

 of the skull to the spinal column is quite different from that of one 

 part of the vertebral column to another. 



The fallacy involved in the vertebral theory of the skull is like that 

 which, before Von Bar, infested our notions of the relations between 

 fishes and mammals. The mammal was imagined to be a modified 

 fish, whereas, in truth, fish and mammal start from a common point, 

 and each follows its own road thence. So I conceive what the facts 

 teach us is this : the spinal column and the skull start from the 

 same primitive condition a common central plate with its laminae 

 dorsales and ventrales whence they immediately begin to diverge. 



The spinal column in all cases becomes segmented into its soma- 

 tomes ; and, in the great majority of cases, distinct centra and in- 

 tercentra are developed, enclosing the notochord more or less 

 completely. 



The cranium never becomes segmented into somatomes ; distinct 

 centra and intercentra, like those of the spinal column, are never de- 

 veloped in it. Much of the basis cranii lies beyond the notochord. 



In the process of ossification there is a certain analogy between 



