My interest increased with the extent of my observations, until, for several years, I abandoned practical medicine for the exclusive study of the science of the brain in the great volume of nature, with the doctrines of Gall as the basis of the investigation. As it was my purpose to seek the deficiencies as well as the merits of the new science, I tested its accuracy by the careful examination of living heads and skulls in comparison with ascertained character, and with the anatomy of the brain, not forgetting the self-evident principles of mental philosophy. Many thousand critical examinations were made between the years 1834 and 1841, leading to many positive conclusions. The first year's observations made me distinctly aware and certain of several defects in the doctrines, as to the functions ascribed to certain localities of the brain to which were ascribed, Mirthfulness, Acquisitiveness, Adhesiveness, Constructiveness, Tune, Ideality, Combativeness, Destructiveness, and Cautiousness. The functions of these localities were evidently misunderstood, and the faculties erroneously located. The external senses were omitted from the catalogue of cerebral organs, though evidently entitled to recognition, and the physiological powers of the brain, the prime mover and most important part of the constitution, were almost totally ignored. Following the old route of exploration by cranioscopy, I sought to supply these defects. I found the supposed Mirthfulness to be a planning and reasoning organ, and the true Mirthfulness to be located more interiorly. Acquisitiveness was evidently located farther back. The so-called organ of Adhesiveness appeared to be incapable of manifesting true friendship, and its absence was frequently accompanied by strong capacities for friendship, of a disinterested character. Constructiveness appeared to be located too low, and too far back, running into the middle lobe, which is not the place for intellect. Tune did not appear to correspond regularly to musical talent. Many of the higher functions ascribed to Ideality were conspicuous in heads which had that organ small, with a large development just above it. Combativeness had evidently less influence upon physical courage than was supposed, for it was sometimes well developed in cowards, and rather small in brave men. Cautiousness was evidently not the organ of fear, for the bravest men, of whom I met many in the southwest, sometimes had it in predominant development, and in the timid it was sometimes moderate, or small. Destructiveness was frequently a characteristic of narrow heads (indeed this is the case with the Thugs of India), and a broad development above the ears was sometimes accompanied by a mild disposition. The height of the head above the ears did not prove a correct criterion of moral character, nor did the breadth indicate correctly the amount of the selfish and violent passions.