. Text book of zoology. Zoology. Class 6. Mammalia. 473 sacrum; the false ribs, shorter. The sternum, which is almost always long and narrow, consists at first of a cartilaginous mass, in which a series of ossifications appears later; the latter usually remain separate throughout life, so that the adult sternum retains a jointed appearance ; occasionally they fuse to a great extent (as in Man), The most anterior joint, the manubrium, is generally somewhat broader than the succeeding ones; to this the first pair of ribs are attached, whilst the other true ribs are attached at the junctions of t
. Text book of zoology. Zoology. Class 6. Mammalia. 473 sacrum; the false ribs, shorter. The sternum, which is almost always long and narrow, consists at first of a cartilaginous mass, in which a series of ossifications appears later; the latter usually remain separate throughout life, so that the adult sternum retains a jointed appearance ; occasionally they fuse to a great extent (as in Man), The most anterior joint, the manubrium, is generally somewhat broader than the succeeding ones; to this the first pair of ribs are attached, whilst the other true ribs are attached at the junctions of the other joints. The last joint, the xiphisternum {processus xiphoides), with which no ribs are connected, usually ends in a broad cartilaginous plate. Only in the Monotremes is there an episternum corresponding with that of Reptiles, as in many Lizards it is here a large T-shaped bone. The skull of the adult consists chiefly of bone, and exhibits but little cartilage. Not only the small premaxilla and the large maxilla, but also the bones belonging to the upper' portion of the gill-bars, are fused with the skull. Of these only the palatine, which is attached anteriorly to the premaxilla, and the somewhat small pterygoid are present, whilst the quadrate has dis- appeared (or at least in its usual form, see below under the ear) ; the lower jaw, which consists of a single bone on each side, articulates directly with the skull. The two rami are either united anteriorly by means of connective tissue, or (in the adult) are anchylosed (Horse, Man, and others). There are two occipital condyles instead of one as in Reptiles and Birds. There is no interorbital septum as in many Reptiles, etc.; the cranial cavity extends forwards as far as the nasal cavities. The latter are usually very well developed; they are separated by a plate, at first cartilaginous, later partially replaced by bone, which arises from the anterior wall of the skull, and projects forwards. They are also at first sur
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
