The origins of the first six dorsal nerves correspond to the interval between the sixth cervical and the fourth dorsal spines.
The origins of the six lower dorsal nerves correspond to the interval between the fourth and the eleventh dorsal spines.
The origins of the five lumbar nerves correspond to the interval between the eleventh and twelfth dorsal spines.
The origins of the five sacral nerves correspond to the spines of the last dorsal and the first lumbar vertebræ.
57. Movements of the spine.—The movements of which the spine is capable are threefold: 1. Flexion and extension; 2. Lateral inclination; 3. Torsion. Flexion and extension are freest between the third and the sixth cervical vertebræ, between the eleventh dorsal and the second lumbar, and between the last lumbar and the sacrum. This is well marked in severe cases of opisthotonos, where the body is supported on the back of the head and heels.[4]
Still better may it be observed when a mountebank bends backwards, and touches the ground with his head.
The lateral movement is freest in the neck and the loins.
The movement of torsion or rotation round its own axis may be proved by the following experiment:—Seated upright, with the back and shoulders well applied against the back of a chair, we can turn the head and neck as far as 70°. Leaning forwards so as to let the dorsal and lumbar vertebræ come into play, we can turn 30° more.
58. Position and motions of scapula.—There are a few points worthy of observation about the scapula. It covers the ribs from the second to the seventh inclusive. We can feel its superior angle covered by the trapezius. The inferior angle is covered by the latissimus dorsi, which keeps it well applied against the ribs in the strong and athletic; but in weak and consumptive persons the lower angles of the scapulæ project like wings—hence the term ‘scapulæ alatæ.’
A line drawn horizontally from the spine of the sixth dorsal vertebra over the inferior angle of the scapula gives the upper border of the latissimus dorsi. Another line drawn from the root of the spine of the scapula to the spine of the last dorsal vertebra gives the lower border of the trapezius, which stands a little in relief.