yet nothing more effectual; the canal which traverses each vertebra, is not of the same uniform diameter throughout, but is much larger at each end of the bone, whence it contracts gradually to the centre; its diameter at the centre is just adapted to the size of the cord and its sheath; but at each extremity it is much larger than would be needed, were no flexures of the whole column to be made. The annexed rough diagram supposes a section of

two cervical vertebræ. A, the vertebræ ; B, the spinal canal; c, the spinal cord. Now, the central narrowness and the gradual expansion of the canal through each vertebra, tend to accomplish the following objectnamely, the susceptibility of a great flexure of any two given vertebræ at their joint, without compressing the spinal cord, and indeed without bending it in an equal ratio; in fact, the

diameter of the canal at the flexure is not reduced beyond that of its narrow portion. Thus is the safety of the bird provided for, and the needful mobility of the neck preserved. From the experiments of Mr. Earle, it was found that the vertebræ thus constructed, might be bent backwards even to a right angle, and laterally to the extent of half a right angle, without injury to the inclosed spine.

It is in facts like this-in minute details of structure, easily comprehended by the most ordinary intellect-that the power and wisdom of God are so clear and palpable. When we attempt to grasp mentally the great scheme of creation, weigh the bearings of one portion on another, and moot the final causes of organic life, our mind recoils from the task; we feel our weakness, and are lost in amazement. But when we come to the examination of structure, and at every step meet with proofs of care, skill, and design, we feel delighted and refreshed as we pursue our way, and trace the hand of God in the works of this lower world. So, too, is it when we contemplate the scheme of salvation; the truths essential for us to know and believe are clear and direct, and are cal

culated to strengthen and refresh us in our journey through life. Plain is the gospel plan as unfolded to us; but its great mysteries are beyond the utmost stretch of our minds-these we see through a glass darkly; in vain we try to penetrate into the secrets of the Eternal Mind. Let it suffice us that all that is needful is revealed; and that those things which now we know not, we shall know hereafter.

CHAPTER VII.

THE SPINAL COLUMN OF REPTILES.

LEAVING the birds, the various reptile tribes next demand our notice. The difference in form and habits between the numerous groups into which the reptiles are divided is very great. Some have four limbs, some only two, and some none. Some are clad in strong armour, some are clad with scales, and some are naked. Some are terrestrial, some aquatic, and some arboreal. Some dart along with wonderful rapidity, others are sluggish and heavy in their movements. Many are capable of writhing and twisting their forms into various curves or flexures; others have no movements excepting those of the head and limbs. Under all these circumstances great modifications in the character of the spine may be expected, and nothing affords a more decided contrast than that of the tortoise compared with that of the serpent.

Few persons who look at a tortoise consider that the shell, as it is termed, into which the animal can withdraw its limbs and head, consists, in reality, of a great portion of the skeleton developed externally, and modified into a box or case in which the muscles, the bones of the shoulders, and hips, and the viscera are inclosed; this box is covered with horny plates, sometimes with a leathery membrane. The arched upper portion of this case is termed the carapace, the lower is called the plastron. Now let us see what the carapace really is, and of what it is composed. If we remove the plastron, we at once perceive the dorsal portion of the spinal column running down the centre of the concave inside of the carapace, and consolidated to it so as to be immovable; the individual vertebræ, however, may be readily distinguished-they are small and elongated. On looking more narrowly, and supposing the horny plates on the outside to be removed, we find a series of bones, united together by suture like those of the human skull, running down the central portion of the carapace-these bones are the processes of the vertebræ thus strangely altered from their ordinary form and appearance. On each