. Comparative anatomy and physiology. 202 COMPARATIVE ANATOMY AND PHYSIOLOGY. more (in Lepidosteus eight or nine) longitudinal rows of pocket-like valves; in Lepidosteus there are four well-developed and four smaller valves in each of the nine planes, so that were they all complete there would be as many as seventy-two. Among the Dipnoi, Ceratoclus has one or more rows of well- developed pocket valves, but the fact that the number is inconstant shows that a change is impending; such a change is found in Protop- terus, where the valves are few in number and minute in size, while their place is
. Comparative anatomy and physiology. 202 COMPARATIVE ANATOMY AND PHYSIOLOGY. more (in Lepidosteus eight or nine) longitudinal rows of pocket-like valves; in Lepidosteus there are four well-developed and four smaller valves in each of the nine planes, so that were they all complete there would be as many as seventy-two. Among the Dipnoi, Ceratoclus has one or more rows of well- developed pocket valves, but the fact that the number is inconstant shows that a change is impending; such a change is found in Protop- terus, where the valves are few in number and minute in size, while their place is taken by a longitu- dinal fold, which extends down the greater part of the cone, and very possibly owes its origin to a fusion of a row of valves. By means of the valve the cone is divided into a right and a left half, and the blood that has just returned from the body is now carried to the third and fourth arches, the latter of which gives off a large pulmonary artery, or vessel which goes direct to the lungs. The essential parts of this ar-. Fig. 87.—Diagram of the Arterial Circu- lation in Fishes. (AfterWiedersheim.) rangement are seen among some of the Amphibia ; but, as may be sup- posed from what has already been said of the arrangement of the ventricle in the lower Reptilia, no functionally independent arterial cone is to be observed in them ; nor is it seen in the adults of the higher Vertebrates, though even there it is at first a distinct part of the heart, and is undivided both within and Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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