. Elementary text-book of zoology. Zoology. 142 PISCES. the moveable supporting bones of the upper and lower jaws (Labroidert). The buccal cavity is distinguished by its width, and by the great number of teeth it contains, which are developed from the papilla? of the mucous membrane by dentinal ossification. There are often two curved parallel rows of teeth on the upper jaw; an outer row on the prenmxilla, and an inner row on the palatine, and there may also be a median unpaired row on the vomer. On the lower jaw there is only one curved row of teeth. There may also be teeth on the hyoid arch
. Elementary text-book of zoology. Zoology. 142 PISCES. the moveable supporting bones of the upper and lower jaws (Labroidert). The buccal cavity is distinguished by its width, and by the great number of teeth it contains, which are developed from the papilla? of the mucous membrane by dentinal ossification. There are often two curved parallel rows of teeth on the upper jaw; an outer row on the prenmxilla, and an inner row on the palatine, and there may also be a median unpaired row on the vomer. On the lower jaw there is only one curved row of teeth. There may also be teeth on the hyoid arch and on the upper jaw (maxilla?) and para- sphenoid, and, as a rule, on the branchial arches also, especially on the upper and lower pharyngeal bones. The teeth are distinguished according to their shape into pointed conical prehensile teeth and grinding teeth. A small, hardly moveable tongue is developed on the floor of the buccal cavity, and the At lateral walls of the pharynx are pierced by the gill slits. Fol- lowing the pharyn- geal cavity, there is a usually short, funnel- FIG. 592, longitudinal section through the SnaPecl WSOphagUS, and head of a larva of Pttromyzon (after Balfour). N, nervous a large stomach, which system; ('«, nutochord; Ot, auditory vesicle (represented JQ f j-i i as visible) ; O, month; T>, velum ; H, thyroid involution ; eCl11' ILS, lirnnchial pouches; C, heart; , optic vesicle; out into a CftX'lim of Ol, olfactory pit. • n , •• considerable size (fig 501). Ctt'cal appendages (pyloric appendages] are not unfrequently met with at the entrance to the longer mid-gut (small intestine) which is marked off by a valve ; they probably serve the purpose of increasing the extent of the secreting surface of the alimentary canal. The intestine is usually several times coiled, and its internal surface is remarkable for the longitudinal folds of the mucous mem- brane ; villi such as are found in the higher Vertebrates are only rarely pre
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
