SIDE VIEW OF LION’S SKULL.
a.m, auditory meatus; b.ty, bulla tympani; j, jugal arch or zygoma; o.c, occipital condyle for the articulation of the skull with the first vertebra; c, condyle of the lower jaw; g, glenoid cavity with which the condyle of the lower jaw articulates; p, the bony clamp, or paroccipital process.
Closely pressed against the hinder wall of this bulla is a sort of bony clamp, which seems to keep the bulla in its place, and running obliquely along the surface of the swelling is an indistinct groove, corresponding to which, in the interior of the drum, is a bony wall, dividing the drum cavity into an inner and an outer compartment, these two divisions being formed from separate bones, as an examination of a very young skull will show.
The almost globular form and great relative size of the bulla tympani; the absence of any distinct bony passage leading from its cavity to the interior, the opening being quite flush with the wall of the drum; and the division of the cavity into two parts by a bony partition, are all very important as distinctive characters of the Cat family, and also, with lesser modifications, of the whole Æluroid group.
UNDER VIEW OF LION’S SKULL.
The letters have the same significance as in the side view.
The power of retracting the claws, so characteristic a feature of all the true Cats (which are, without exception, digitigrade), is brought about by certain peculiarities of structure of the last two joints of the toes. Of the three phalanges, or bones which make up the skeleton of the toe, the first, or that nearest to the wrist or ankle, is of the ordinary shape: about three times as long as broad, with a regular cylindrical shaft, and pulley-like ends, for articulation with the bone to which it is joined. The second, or middle phalanx, is pretty much like the first, except that its shaft is scooped out on one side, so as to make a greater distance between it and the corresponding bone of the next toe than there would otherwise be. The third and last joint, called the ungual phalanx, from the fact of its supporting the claw, has the regular pulley-surface to articulate with the preceding joint, but its farther end is strongly curved downwards and pointed at the end; it has, in fact, the shape of the horny talon of which it forms the supporting core. Further support is afforded to the claw by an outgrowth of the phalanx, which commences near its articular end, and grows over the end of the claw like a sort of hood, thus giving the ungual phalanx of the Cat a most peculiar and unmistakable shape. Between the upper surfaces of the last phalanx and the last but one passes a strong and very elastic ligament, which so pulls upon the ungual phalanx as to bend it on its predecessor, and so cause the two to be almost parallel, the hood of the claw-bearing bone being received between the preceding joint of its own toe and that of the next; hence the scooping out of the middle phalanges. Thus, by the action of this ligament, the claw under ordinary circumstances is pulled back within its covering of skin, which forms for it a sort of protecting pouch, and effectually prevents its being worn down by rubbing against the ground. But when the Cat strikes its prey, it bends the paw upon the wrist by means of the strong flexor (or bending) muscles, which are placed along the under surface of the fore-arm and hand. The end of the string-like tendons of one of these muscles divides into four slips, one for each toe, and, running along the under surface of the first two phalanges, is inserted into the corresponding surface of the third, and, this under surface being bent upwards by the elastic ligament, the tendon is, when the claw is retracted, put upon the stretch. But when the flexors come into play, they pull upon the ungual phalanx, causing it to turn through a quarter-circle upon its articulation, and thus protruding the claw from its pouch. Immediately the flexors relax the elastic ligament is again allowed to act, and the claw springs back into its place of repose.
TENDONS AND LIGAMENTS OF A CAT’S TOE.
(Twice Natural Size. From a Sketch by T. J. Parker.)