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Show 1876.] FEET OF CERTAIN MAMMALS. 533 much expanded as to project considerably beneath the toes. The toes are very short and have feeble claws. The ball of the thumb covering the metacarpophalangeal joint is also much expanded and flattened. Tins remarkable condition of the sole of the foot and of the thumb is seen, on examination by the microscope, to be due to the great development of the integument and areolar tissue. In these Bats the feet are undoubtedly adhesive, enabling them to walk on smooth hard surfaces, where the claws could afford but slight aid in progression ; but the adhesive power is evidently much inferior to that possessed by Thyroptera ; nevertheless the difference in structure between the comparatively simple adhesive sole of the foot and thumb of V. pachypus, and the highly differentiated sucking-cups of T. tricolor is one of degree only. The walls of each cup are composed, from without inwards, 1, of skin (continuous with the integument of the thumb); 2, of a middle layer of connective tissue with cartilage cells and glandular tissue; and, 3, of a thin epithelial layer lining the concavity of the cup, having on its surface the openings of glands, which are most abundant near the margin of the disk. The middle layer at the base of the cup, for a short distance around the point of its connexion with the short pedicle which attaches it to the thumb, consists almost entirely of cartilage ceils, which soon become considerably thinned out and replaced by another form of connective tissue. This connective tissue, which forms the greater part of the walls of the suctorial disk, lying (as already described) between an outer and inner* layer of integument, appears to consist of two layers, that lying next the external integument being very dense and having a few cartilage cells, while the inner layer lying next the thin epidermis lining the cup consists of rather broad fibres radiating from the cartilaginous base of the cup towards its circumference, and which cause a corresponding radiating appearance in the cuticle lining the concavity of the cup (see Plate LV. fig. 5). These radiating fibres no doubt suggested to Sefior Jimenez de la Espada the idea of a muscular apparatus ; but, as I have already remarked, no trace of muscular tissue can be detected in them or in any other part of the disk. They are about T^Q- of an inch in diameter and extend from the cartilaginous base of the disk outwards to within a short distance from its free margin, being separated from each other by a thin layer of connective tissue derived from the outer part of the middle layer. Examined under high powers and with an immersion-lens, they appear solid and almost structureless f. Although they do not present the characters of ordinary elastic * The terms " outer " and " inner," used with reference to the suctorial disk, refer to its convex and concave surfaces, which I here, for convenience, consider its outer and inner sides respectively. t Prof. Turner has kindly examined these radiating fibres for m e ; he says:- " With careful focusing I think that I can recognize traces of structure in each fibre; there are appearances of very minute elongated nuclei, such as one sees in tendon I a m disposed, on the whole, to regard them as a modification of connective tissue, though not elastic." Prof. Turner means by this that they do not present the characters of what is commonly known as clastic tissue. |
