Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 112 VERTEBRATA. form the brain and with the first portion of the alimentary canal. The canal formed by the neural arches is here dilated to form the cranial capsule, on the ventral side of which are placed cartilaginous arches known as the visceral arches, of which the anterior pair constitutes the mandibular apparatus, is armed with teeth and surrounds the entrance to the alimentary canal (fig. 571). The mandibular arch is followed by a number of arches which surround the pharynx; the f
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 112 VERTEBRATA. form the brain and with the first portion of the alimentary canal. The canal formed by the neural arches is here dilated to form the cranial capsule, on the ventral side of which are placed cartilaginous arches known as the visceral arches, of which the anterior pair constitutes the mandibular apparatus, is armed with teeth and surrounds the entrance to the alimentary canal (fig. 571). The mandibular arch is followed by a number of arches which surround the pharynx; the first of these is the hyoid arch and the rest are the branchial arches. The part of the body behind the head may be divided into two regions: (1) an anterior region—the trunk proper—in which the peritoneal or body cavity lined by the peritoneal membrane is placed ; the vertebras in this region bear ribs ; (2) a posterior region or tail, FIG. 571. —Head and anterior region of the vertebral column of Acunthiux (after Owen). £, Body of vertebra; O, neural arch; S, intercalated piece; P'j, Palatoquadrate; LI-, labial cartilage ; Zb, hyoid arch ; Kb, branchial arch; 8g, shoulder-girdle. in which there is no body cavity, and the hsemapophyses unite with each other to enclose a canal (containing the caudal vessels). This, the most simple form of segmentation of the trunk, is confined to the lower Vertebrates which propel themselves by the flexion and undu- latory movements of the vertebral column, and, like the Annelids, live in water, in inud, or in the earth, or even creep after the manner of snakes on the surface of the earth. In the higher Vertebrates, however, in which, as in the Arthropods, the function of locomotion is discharged by paired appendages, the movements of the chief axis are reduced and in many regions are altogether absent. In the Vertebrata there are only two pairs of limbs, an anterior pair and a posterior pair. In the lower Verte- brata they have the fo
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