The croonian lecture. On the internal structure of the human brain, when examined in the microscope, as compared with that of fishes, insects and worms

In this lecture the author pursues his researches respecting the anatomy of the human brain, and compares it with that of fishes, insects, and worms, in the hope of developing the connexion between the action of the nerves and the motion of the muscles. To obviate the sources of error attendant upon the usual methods of dissecting and examining the brain, a portion of it in a very recent state was submitted to the microscope, after having been immersed in distilled water. Rows of globules were thus detected passing in straight lines from the circumference of the cortical substance into the medullary portion, the appearance of which is shown by Mr. Bauer in an annexed drawing. From a representation, also by Mr. Bauer, of the tench, it appears that its relative proportion to the size of the animal is smaller than in the bird, —that it has a central cavity and a nodulated basis. In insects the brain contains, and its principal portion is connected by, nervous chords, with what is usually called a ganglion, but which, when examined accurately, is found to resemble the brain in texture, and which, from the office of the nerves it sends off, the author considers, asMedulla oblongata . Below this is a regular line of ganglions united by a double nerve, the details of these structures being illustrated by annexed drawings. Among insects the bee has the largest proportion of brain relative to the size of its body. In the moth and caterpillar it is smaller, but similar in structure, as also in the lobster. In the garden snail the brain is relatively larger than in the bee, but there are no ganglions, although the structure of theMedulla spinalis is the same.