. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 410 ANATOMY OF VERTEBRATES. denticles and sieve-like plates or processes, fig. 85, 6?, to prevent the entry of food into the interspaces of the gills, and the branchial 276. Digestive organs in situ., Planirostra. ,v t'^; •-- outlets are guarded by valves which reciprocally prevent the regurgitation of the respiratory streams back into the mouth. The necessary cooperation of the jaws with the hyoid arch in the rhythmical movements of respiration is incompatible with protracted maxillary mastication ; and, accordingly, th
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 410 ANATOMY OF VERTEBRATES. denticles and sieve-like plates or processes, fig. 85, 6?, to prevent the entry of food into the interspaces of the gills, and the branchial 276. Digestive organs in situ., Planirostra. ,v t'^; •-- outlets are guarded by valves which reciprocally prevent the regurgitation of the respiratory streams back into the mouth. The necessary cooperation of the jaws with the hyoid arch in the rhythmical movements of respiration is incompatible with protracted maxillary mastication ; and, accordingly, the branchial apparatus renders a compensatory return by giving up, as it were, the last pair of its arches to the completion of the work which the proper or anterior jaws were compelled by their services to re- spiration to leave unfinished : and thus the mouth of typical Fishes is closed at both ends by dentigerous jaws.' The first joortal to the alimentary tract is usually formed by the ujjper and lower jaws, fig. 276, «, b, and their teeth: the Gym- nodonts are so called on account of their conspicuous manifestation of tliis character, fig. 258. In most Fishes the jaws are covered by the skin, which, in passing into the mouth, takes on the character of the mucous membrane. In some Fishes the inteeu- ment is folded before passing over the jaws, and the arched and fortified barrier is preceded by a fosse inclosed by fleshy lips. The Wrasses (Lahrida;), Mullets (^JMugiliclcE), and the Carp-tribe (^Cyprinidce) exemplify this character. In Crenilabrus, Champs, and Julis, the lips are plicated. In Mi/r/il laheosus the thick upper lip has a transverse fold. In some Ci/prinida the laliial organs are developed to excess, as, for example, in the genus thence termed Labeoharhua, in which the lips are not only unusually thick and fleshy, but the lower one is produced downward like a pointed beard : it forms a long cone in Mormi/rus Pctcrsii. The labiated Fishes have not, however, so d
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