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CHAPTERS XV. AND XVI.
PLATE XXX. -FORE EXTREMITY OF THE MOLE-HEAD OF THE
ELEPHANT-FINGER-LIKE EXTREMITY OF THE PROBOSCIS-SECTION OF THE PROBOSCIS-BAT'S WING BILL OF THE PARROT EYES OF INSECTS-EYES OF A SPIDER.
Fig. 1. Is the fore extremity of the mole; a, the os humeri, is peculiar, not only for its shortness, but in being articulated by b, one head to the scapula, and by c, another to the clavicle ; it is altogether of such a nature as to turn the palm outwards for working.
The foot, or we may name it the hand, has eleven bones in the carpus or wrist, which is two more than the carpus of man. One of which, d, is remarkable, and from its shape is called the falciform bone; it gives the shovel form to the hand.
Fig. 2. The head of the Elephant.
Fig. 5. A transverse section of the proboscis, showing, a, a, the two tubes or nostrils. Between the external integuments and the tubes are two sets of small muscles ; an inner one running in a transverse, and an outward one in a longitudinal direction : b, b, the transverse faciculi of muscles, some of which run across the proboscis, others in a radiated, and some in an oblique direction : C, C, the radiated, and d, d, the oblique fibres approximate the skin and the tubes, without contracting the cavity of the latter. The others, which pass across the proboscis, contract both the surface of the organ, and the canals it contains ; they can, at the same time, elongate the whole or a part of it : e, e, the longitudinal faciculi, forming four large muscles, which occupy all the exterior of the organ.
Fig. 6. The extended wings of the bat. Ostrologically considered, they are hands, the bony stretches of the membrane being the finger bones extremely elongated : a, a, the thumb, is short, and armed with a nooked nail, which these animals make use of to hang by, and to creep. The hind feet are weak, and have toes of equal length, armed also with hooked nails; the membrane constituting the wing, is continued from the feet to the tail.
Fig. 7. The upper mandible of the parrot, which is articulated with the cranium by an elastic ligament, admitting of a considerable degree of motion.
Fig. 8. An eye compounded of a number of lenses. The eyes of insects differ widely from vertebrated animals, by being incapable of motion ; the compensation, therefore, is a greater number of eyes, or an eye compounded of a number of lenses. Hook computed the lenses in a horse-fly to amount to 7,000, and Leuwenhoek found the almost incredible number of 12,000 in the dragon-fiy.
Fig. 9. The eyes of a spider, drawn from nature. The number of eyes in insects varies from two to sixteen. The spider here referred to answers the description of the garden spider, (Epeira Diadema,) the eyes of which are planted on three tubercles, four on the central one, and two on each side of the lateral ones.
PLATE XXXI. - THE CHAMELEON, AND INTESTINE OF THE
Fig. 1. The chameleon, drawn from one of the species preserved in the Anatomy School, Christ Church, Oxford. The eyes of this creature are very peculiar: they are remarkably large, and project more than half their diameter. They are covered with a single eye-lid, with a small opening in it opposite the pupil. The eye-lid is granulated like every part of the surface of the body, with this difference, over the eye the granulations are disposed in concentric circles which form folds in that part to which the eye is turned: and as the lid is attached to the front of the eye, so it follows all its movements. The neck is not “inflexible, but its shortness, and the structure of the cervical vertebræ exceedingly limit the motion; this, however, is admirably compensated by the not less singular local position than motion of the eye, as the animal can see behind, before, or on either side, without turning the head.
Fig. 2. The spiral intestine of the sea-for cut open; taken from a preparation in the museum of the Royal College of Surgeons, London. The sea-fox is not, as Paley supposes, a “quadruped ; but a species of shark, (squalus vulpes.) The convoluted intestinal tube is also found in some other genera of fish. In this specimen the internal membrane is converted into a spiral valve, having thirty-six coils ; so that the alimentary substances, instead of passing speedily away, by proceeding round the turns of the valve, traverse a very considerable circuit: an extensive surface for the absorbents is thus provided.
FIG. 3. The spiral valve removed, showing the mode of its coiling.