This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
When we desire to gain a general idea of the structural plan of any object we examine, if possible, sections made through it in different directions ; the botanist cuts the stem of the plant he is examining lengthwise and crosswise, and studies the surfaces thus laid bare ; a geologist, investigating the structure of any portion of the earth's crust, endeavors to find exposed surfaces in canons, in railway cuttings, and so forth, where he may see the strata exposed in their natural relative positions ; and the architect draws plans which show to his clients sections of the building which he proposes to erect for them; so, also, the best method of getting a good general idea of the way in which the parts of the human body are put together is to study them as laid bare by cuts made in different directions ; this gives us a general outline and the details may be filled in afterwards.
If the whole body were divided from the crown of the head to the lower end of the trunk, and exactly in the middle line, so as to separate it into right and left halves, we should see something like Fig. 1, if we looked at the cut surface of the right half. Such a section shows us, first, that the body fundamentally consists of two tubes or cavities, separated by a solid bony partition. The larger cavity, b, c, known as the ventral or hoemal cavity, lies on the front side, and contains the greater part of the organs concerned in keeping up the blood flow (organs of circulation), in breathing (organs of respiration) and in digesting food (organs of digestion). It does not reach up into the neck, but is entirely confined to the trunk. The smaller cavity, a, a', is tubular in the trunk region, but passes on through the neck, and widens out in the skull; it is known as the dorsal or neural cavity, and contains the most important nervous organs, the brain, N', and spinal cord, N. In the partition between the two cavities is a stout bony column, the backbone or spine, e, e, which is made up of a number of short thick bones piled one on the top of another.
How do we start by preference to gain a knowledge of the structural plan of any mass of matter? Give examples. Apply to the study of human anatomy.
What should we see on examining the cut surface of a human body divided into right and left halves? What organs lie in the haemal cavity? What in the neural? How far does the haemal cavity extend toward the head ?