. Text book of zoology. Zoology. Glass 2. Pisces. 363 may be present but are less constant. In the Dipnoi some of these bones occiu' biit cartilage persists to a large extent. In the cartilaginous Ganoids, as already mentioned, only membrane bones are found, among them a parasphenoid, frontals, parietals, and several smaller bones Fig. 300. Skull of a Perch, A dorsal, B ventral. 1 frontal, 2 prefrontal, 3 ethmoid, 4 postfrontal, 5 basioceipital, 6 parasphenoid, 7 parietal, 8 supraoooipital, 9 epiotic, 10 exoooipital, 11, prootio, 12 squamosal, 13 opisthotic, 14 alisphenoid, 16 vomer.
. Text book of zoology. Zoology. Glass 2. Pisces. 363 may be present but are less constant. In the Dipnoi some of these bones occiu' biit cartilage persists to a large extent. In the cartilaginous Ganoids, as already mentioned, only membrane bones are found, among them a parasphenoid, frontals, parietals, and several smaller bones Fig. 300. Skull of a Perch, A dorsal, B ventral. 1 frontal, 2 prefrontal, 3 ethmoid, 4 postfrontal, 5 basioceipital, 6 parasphenoid, 7 parietal, 8 supraoooipital, 9 epiotic, 10 exoooipital, 11, prootio, 12 squamosal, 13 opisthotic, 14 alisphenoid, 16 vomer.—After Cuvier and Valenciennes. The dorsal membrane bones of the head are in many Fish very superficial in position, covered only by a thin layer of connective tissue and epidermis (Stui-geon, bony G-anoids, many Teleosteans); in others, the overlying connective tissue is thicker. A large number of Tisceral arches* usually seven pairs, occasionally more (some Sharks), are suspended from, or situated near to, the skull. The members of the first pair are united ventrally, whilst the others are attached to a series of unpaired, cartilaginous, or bony pieces (basibranchials). The most anterior, the mandibular arch, consists, in the Sharks, of an upper and a lower cartilaginous piece; the former, which is connected in front with the corresponding one of the other side, is termed the p a 1 a t o - quadrate, or less happily, the upper jaw; the latter, the mandibular cartilage, or lower jaw. The two portions are jointed together. The mandibular arch, the best developed, is loosely connected with the skull in the Sharks, and forms the framework of the mouth. The second, the hyoid, is similarly divided into two parts ; the upper is fastened to the skull above, whilst its lower end is attached by connective tissue to the mandibular. The other * The Cyolostomi are excluded from this <ieeeription of the visceral arches, arrangements in this group are much modified and difficult to unde
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
