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On its outer side is afterwards formed the upper-jaw bone, in the narrower sense, while the middle part of the skeleton of the upper jaw, the intermaxillary, develops from the foremost part of the frontal process. The two upper-jaw processes are of great importance in the further development of the face.
The last tooth, or dens sapientiæ, of the upper jaw most frequently decays first, and is liable to produce pain over the eye and temple of that side. The last tooth of the under-jaw is also liable to produce a similar hemicrania, when it begins to decay. When a tooth in the upper-jaw is the cause of the headach, a slighter pain is sometimes perceived on the cheek-bone.
Head of a chick embryo, four days old, from below. n nasal pit, o upper-jaw process of the first gill-arch, u lower-jaw process of same, k double apostrophe second gill-arch, sp choroid fissure of eye, s gullet. Heads of chick embryos: 2.309 from the end of the fourth, 2.310 from the beginning of the fifth week. There is little to be said of the development of the lower sense-organs.
After the upper-jaw came the lower-jaw and throat, with the tongue. This last was an enormous mass of fat, about as large as an ox, and it weighed fifteen hundred or two thousand pounds. After this was got in, the rest of the work was simple. The blubber of the body was peeled off in great strips, beginning at the neck and being cut spirally towards the tail.
Above at the basis a small process grows out of this first gill-arch; this is the upper-jaw process. The upper-jaw process forms the chief part of the skeleton of that jaw, the palate bone, and the pterygoid bone.
Then came the fins, and after them the upper-jaw, with the whalebone attached to it. The "right" whale has no teeth like the sperm whale. In place of teeth it has the well-known substance called whalebone, which grows from the roof of its mouth in a number of broad thin plates, extending from the back of the head to the snout.