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The auditory nerve proceeds first to the lowest or hindermost portion of the brain, known as the bulb, or medulla oblongata; thence a continuation of the nerve tract passes forward to a central region, the posterior corpora quadrigemina, then, by a new relay of nerve-fibres, to the highest and most important part of the brain, that most closely associated with consciousness, the cortex of the temporal lobe, where there is situated the most important of all the centres of hearing.
So that the correspondence in general structure, in the minute structure of the tissues, in chemical composition and in constitution, between man and the higher animals, especially the anthropomorphous apes, is extremely close. Shows a human embryo, from Ecker, and a dog embryo, from Bischoff. Labelled in each are: a. Fore-brain, cerebral hemispheres, etc. b. Mid-brain, corpora quadrigemina. c.
On account of the great size of the cerebrum, the midbrain is entirely concealed from view when the other parts occupy their normal positions. The midbrain carries upon its back and upper surface four small rounded masses of cell-bodies, called the corpora quadrigemina.
It is just the reverse in the higher Vertebrates, in which the first and third sections, the cerebrum and cerebellum, are exceptionally developed; while the middle brain and after brain remain small. The corpora quadrigemina are mostly covered by the cerebrum, and the oblongata by the cerebellum. But we find a number of stages of development within the higher Vertebrates themselves.
The hæmorrhages from anemia are, on the other hand, so frequent, as to explain the majority of such cases as Dr. Clarke's. Meadows observes: "It is not the ovary which is an appendix to the uterus, but the uterus which is an appendix to the ovary." Corpora quadrigemina. Corpora striata. Thalami optici and corpora striata.
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