Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 540 COMPARATIVE ANATOMY. part of the body. This space is gradually reduced in size in the Craniota; it still, however, retains its respiratory function, but many other organs are also differentiated in it; these are, largely, accessory organs for the ingestion of food. Respiratory Ante-chamber (Cephalic enteron). §405. In Amphioxus this portion is bounded, in its most anterior region, which is close to the cavity which carries the mouth, by a ciliated apparatus; there are a number of movab
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 540 COMPARATIVE ANATOMY. part of the body. This space is gradually reduced in size in the Craniota; it still, however, retains its respiratory function, but many other organs are also differentiated in it; these are, largely, accessory organs for the ingestion of food. Respiratory Ante-chamber (Cephalic enteron). §405. In Amphioxus this portion is bounded, in its most anterior region, which is close to the cavity which carries the mouth, by a ciliated apparatus; there are a number of movable processes also at that point, which are directed towards the lumen of the tube, and so prevent the entrance of foreign bodies. The ante-chamber (Fig. 303, d), which occupies about two-fifths of the whole length of the body, has its walls broken through by a large number of obliquely-set clefts ; these form a complicated framework, the sup- ports of which have been already (§ 353) mentioned. The water, which is taken in by the mouth (a), passes through the clefts, and so to the exterior. But as two lateral dermal folds are gradually con- tinued ventrally over the surfaces on which the clefts are placed, and become united below, a peribranchial cavity is formed, which opens by a special pore (c). It should here be remembered that there was something similar to this in the Ascidias (§ 310). But it would not be correct to suppose that the two structures are morphologically identical. A vascular plexus is distributed in the walls of the clefts, the water that streams past effects respiration, the clefts function as branchial clefts, and the whole cavity represents functionally a branchial cavity. There are many special points in this arrangement in Amphioxus, such as the want of symmetry in the branchial frame, and its inde- Fig. 30-t. Vertical median section of a larva of Petromyzon. o Mouth, v Velum. h Ilypobranchial groove. n Spinal chord, ch Notochord. a Otocyst. c Hear
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