From the data which Dr Prichard has given us, in a somewhat scattered form, we shall endeavour to collect and group the most interesting of his facts and opinions. In order to ascertain what modifications of physical structure, variation of climate, food, and habits, may effect upon mankind, it is necessary, first, to review the effects produced by such variation upon domesticated animals. It is indeed questionable whether we can in any case, with certainty, trace these to their native wilds; but, in many cases, we have instances of their return to a savage state, as with the wild horses, goats, oxen, &c.; and although it does not necessarily follow that their conformation, induced by such return, is identical with their original structure, yet there is a reasonable probability that such is the case, and we must take these cases for want of better. How far, then, has the outward form been altered by the changes induced by domestication; how far are instincts acquired by such changes capable of hereditary transmission, and is there any, and what, connexion between the changed instincts and the changed structure? These questions, involving among other things the infant and difficult science of phrenology, Dr Prichard has left very much to conjecture. Whether he considers the data too imperfect, or is afraid of trusting himself with any decided expression of opinion on a subject which has been so obscured by charlatanry, and which is open to so much misapprehension, does not appear; but it certainly is an apparently striking defect, that where a large portion of the work is devoted to the explanation of the different forms of the cranium in the inferior animals and in man, and to which the largest portion of his pictorial illustrations apply, he should give us so little insight into his opinions as to what extent phrenology is fairly entitled to credibility. His having taken so much pains in collecting facts and drawings on this point, necessarily leads to the inference that he attaches much value to the craniological distinctions. We shall take an opportunity presently of recurring to this subject. We will now take some of the most interesting instances, given by Dr Prichard, of structural changes and hereditary instincts, acquired by domesticated animals, and again lost by them on returning to a wild state:--