44 ON THE PLACE OF MAN IN THE SCALE OF BEING. 



ous tube is formed for the lodgment of the spinal cord. The Cranium, which 

 it bears at its upper end, is in reality formed of the same elements as the 

 vertebras, instead of differing from them completely in structure, as we might 

 be led to suppose by examination of its most developed forms only. The 

 object of this enlargement is to enclose the brain, or mass of cephalic ganglia, 

 which attains a greatly increased size in the Vertebrata ; and also to afford 

 support and protection to the organs of special sense, which are far more 

 highly developed among them than elsewhere. The true nature of the cra- 

 nium is best seen in those animals,*in which the brain bears but a small pro- 

 portion to the spinal cord, such as the lower Reptiles and Fishes ; and an 

 examination of its structure in these satisfactorily proves the reality of this 

 view, which is further borne out by the history of its development, and of that 

 of its contained parts, in the higher Vertebrata. 



, 33. The Vertebral column, at its opposite extremity, is usually contracted 

 instead of being dilated, forming a tail, or a rudiment of one, from which the 

 nervous centres are entirely withdrawn ; the development of the tail is com- 

 monly seen to be in an inverse proportion to that of the cranium. To this 

 column, the ribs and extremities are merely apendages, which we find more 

 or less developed in the various tribes, and often entirely absent ; whilst the 

 vertebral column is never wanting, although reduced in some species to a very 

 rudimentary state. It is interesting to compare its various conditions with 

 those which have been noticed in the external skeleton of the Articulata. In 

 the lowest animals of the group, locomotion is pricipally or even entirely per- 

 formed by flexion of the body itself ; and here, as in the warm tribe, we find 

 the skeleton extremely flexible, the whole being comparatively soft, and its 

 divisions indistinct. This is the case, for example, in the Lamprey and other 

 Cyclostome fishes ; in which there is no distinct division into vertebrae, the 

 spinal column scarcely possessing even the density of cartilage. In propor- 

 tion, however, as distinct members are developed, and the power of locomotion 

 is committed to them, we find the firmness of the spinal column increasing, 

 and its flexibility diminishing ; and in Birds, in which, as in Insects, the 

 movements of the body through the air are effected by muscles which must 

 have very firm points of support, the vertebral column is much consolidated 

 by the union of its different parts, so as to form a solid frame-work. As a 

 general rule, then, the mobility of the extremities, and the firmness of the ver- 

 tebral column, vary in a like proportion. The number of these extremities in 

 Vertebrata never exceeds four and two of them are not unfrequently absent. 

 The power of locomotion is not developed to nearly the same proportional ex- 

 tent as in the Articulata ; the swiftest Bird, for example, not passing through 

 nearly so many times its own length in the same period, as a large proportion 

 of the Insect tribes : but it is far greater than that which is characteristic of the 

 Mollusca ; and there is no species that is fixed to one spot, without the power 

 of changing its place. On the other hand, the highest Mollusca approach them 

 very nearly in the development of organs of special sense, of which Verte- 

 brata almost invariably possess all four kinds, sight, hearing, smell, and taste. 

 34. The perfection of the Articulate structure has been shown to consist in 

 the development of those powers which enable the animal to perform actions 

 denoting the highest instinctive faculties. That of the Vertebrata evidently 

 tends to remove the animal from the dominion of undiscerning, uncontrollable 

 instinct ; and to place all its operations under the dominion of an intelligent 

 will. We no longer witness in these operations that uniformity, which has 

 been mentioned as so remarkable a characteristic of instinctive actions. There 

 is evidently, among the higher Vertebrata especially, a power of choice and of 

 determination, guided by a perception of the nature of the object to be attained, 

 and of the means to be employed, constituting the simplest form of the reason- 



