. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. 270 CLASSIFICATION OF VERTEBRATES. Fig. 271. Tooth of ceratodan, Sageno- dus, after Woodward. smaller pair on the vomerine region, while the lower jaw has a pair on the splenial region. The alimentary canal is nearly straight, and is char- acterized by the pres- ence of a well-devel- oped spiral valve (Fig. 40) in the in- testine. Behind, the intestine empties into a cloaca, which also receives, besides the urogenital ducts, median or paired pori abdominales. There are three (J'rotop- terus) or four (Ceratodiis) '^ pairs of
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. 270 CLASSIFICATION OF VERTEBRATES. Fig. 271. Tooth of ceratodan, Sageno- dus, after Woodward. smaller pair on the vomerine region, while the lower jaw has a pair on the splenial region. The alimentary canal is nearly straight, and is char- acterized by the pres- ence of a well-devel- oped spiral valve (Fig. 40) in the in- testine. Behind, the intestine empties into a cloaca, which also receives, besides the urogenital ducts, median or paired pori abdominales. There are three (J'rotop- terus) or four (Ceratodiis) '^ pairs of in- ternal gills, and besides, in the former, external gills (Fig. 269). Besides these, there are present in each swim-bladders which also have respiratory functions. In Cera- todics this lung is single, in Pro- topterus it is paired ; but in both its duct or ducts arise from the ventral surface of the pharynx. Internally these or- gans are sacculated, while the blood comes to it by true pul- monary arteries, which arise either (^Ceraiodus) from the pOS- Fig. 272. Heart and anterior part terior branchial, or (Protoptenis) °f ''^^ '""S^ »* Cemtodus, after Rose. ^ , ,. ^, aortic arches and auricle: c, post- irom the radices aortae. .i- 1 â ; i, .- cardinal vein ; lo^ conus; //i', hepatic The heart has both the sinus veins; /, lung; j, jugular vein; ji, jn- and the atrium partially divided f«â¢"^ jugular vein; oe, oesoph^; /, . , . 1 ^ 1 1 f ^ 1 1 ' 1 pulmonary arteries; 5, subclavian vein into right and left halves bv an , . ° ^ and sinus venosus. incomplete septum, thus fore- shadowing the conditions found in the amphibia, while a true atrio-ventricular valve is lacking. The conus is spirally twisted, and contains several rows of valves, and in Ceratodiis is partially, in Protoptenis completely, divided into venous and arterial halves. I Ceratodiis also has a hyoid pseudobranch (p. 23).. Please note that these images are extracted from scanned page
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