Lastly, we come to the organ of vision, of which, however, there is not much to be said. The differences between the visual organ in the in fant and in the adult consist more in degree than in kind; thus the sclerotic membrane is less elastic, and the cornea is less conical, in conse quence of the smaller quantity of aqueous hu mour; (the greater thickness of this coat is pro duced by the serosity contained between its la minae;) the crystalline lens is less dense, but more convex in form. The pigmentum is in smaller quantity at birth than afterwards; while the retina is thicker and more pulpy than in more ad vanced periods. The yellow tint of the foramen of Soemmering does not become visible till some time after birth, but deepens with the progress of life, till the stage of decline, when it grows paler. It has been ascertained that perfect images are formed on the retina ; and yet for the first few days the child gives no indication of visual sensation, and when objects appear to attract its attention, they are only those which are vividly illuminated. The de ficiency therefore must exist in the optic nerve, though we are ignorant of the organic condition on which this insensibility is dependent. We observe, moreover, that the eye is much more passive than in the adult, that it follows the motion of luminous bodies, or is fixed upon them with little or no apparent interference of the will. This muscular incompleteness, then, tallies with what we have noticed with respect to the other senses. The eye is known in its advance towards manhood to increase in the capability of adapting itself to different distances; but as we are ignorant of the mechanism made use of for this purpose, it is useless to look for cor responding organic alterations. We must not omit to notice those appendages to the appara tus of vision, called eyebrows, which become much more prominent as life advances, by the development of the frontal sinuses, and are therefore better adapted for shading the eyes.
The generative apparatus is situated inter mediately to the animal and the organic system.
The evolution of the organs connected with this function marks the age of puberty; and the changes in which this evolution consists, both in the male and in the female, are too well known to require their specification here. The influence of this development on the mental and moral characters of either sex, is likewise sufficiently familiar even to the most superficial observer.
The human being is related with the external world passively and actively, independently of those organic actions and reactions that are constantly occurring in his system with regard to outward agents. He derives perceptions from objects about him, and he reacts on them by his power of muscular motion. But in his growth we mark that the perfection of those organs, which are scarcely more than passive in his relative life, advances much more ra pidly than those which enable him to take a more active part. Thus the eye and the ear attain a certain maturity of organization and function, long before the bones and muscles, which officiate in locomotion. The bones and
muscles connected with the organs of sensation, and therefore partaking of the passive character, are also equally forward in their development. What is the probable final cause of this arrangement ? If all our voluntary motions were the immediate consequences of our sen sations, as some of them undoubtedly are, such as those which close the dazzled eyes, or refuse the bitter food, or withdraw from pain ful contact;—if all these followed directly on sensations, it would indeed be a strange ano maly, if the systems that belong to each were not precisely on the same level of development. But this is not the case ; all the more impor tant motions, important as it regards that world in which man exists, as an intelligent and social creature, though less so as it respects his individual being, are the results of a mental condition, no less distinct from sensation than from muscular motion. This state is desire, or as it is commonly called when the antecedent of action, will or volition. Probably no men tal state is more simple than this, and it may follow any other. It is therefore the more necessary that it should be preceded by such intellectual changes as will give it a right direction ; in other words, that it should come under the dominion of certain faculties. But in early life the faculties to which we allude are very imperfectly developed; those only have attained any thing like maturity which are in immediate relation with the senses ; such are perception, memory, association, and imagination ; while the reflective faculties, such as comparison, reasoning, abstraction, all in fact that constitute man a judicious expe rienced agent, are rudimentary. The conse quence is that the desires or volitions are pro verbially vain and dangerous. Let us Observe a child of seven years old ; his senses are suffi ciently acute for all ordinary purposes, although they are deficient in precision and delicacy; he has seen many attractive objects, he has heard many wonderful stories, and tasted many exquisite delights; lie remembers them vividly, he associates them rapidly, and often in shapes very different from those in which they were formerly combined. Desires follow which would prompt him to execute the most ridicu lous and mischievous schemes. But happily the muscular system, by which alone he could accomplish them, is too immature and feeble for his puerile purposes. Here then is the final cause that we were in search of; the active corporeal functions of relation must not ad vance beyond the governing faculty of the mind.
But why, it might hastily be asked, should not the senses, the mental faculties, and the motive powers, all have been equally deve loped ? The question is absurd, if we consider but a moment the manner by which the mind accomplishes its growth ; that its higher powers result from the accumulation of innumerable sensations, by which in fact the former are nourished and exercised.