. Text-book of zoology for junior students. Zoology. 2i6 VKKTElSliATR ANHIALS. Tl\e integumentary skeleton is in the furni of placoid scales (fig. I(i4, r)—that is to say, of detached gtains, , or plates. There are two ]> of fins, corresponding to the fore and hind limbs, anil tlie ventral fins are placed far back, close to tlie aims. The heart of an ani'icle and ventricle ; and the hulljiis arteriosus is rhvtlimically contractile, is proviiled with a distinct coat of nmscnlar , and is furnished with sevei'al transverse rows of valves. The gills are fixed, a
. Text-book of zoology for junior students. Zoology. 2i6 VKKTElSliATR ANHIALS. Tl\e integumentary skeleton is in the furni of placoid scales (fig. I(i4, r)—that is to say, of detached gtains, , or plates. There are two ]> of fins, corresponding to the fore and hind limbs, anil tlie ventral fins are placed far back, close to tlie aims. The heart of an ani'icle and ventricle ; and the hulljiis arteriosus is rhvtlimically contractile, is proviiled with a distinct coat of nmscnlar , and is furnished with sevei'al transverse rows of valves. The gills are fixed, and form a number of pouches, which open internally into the pharynx, and mostly conmuinicate with the o\iter world by a series of apei-tnres j)laced on the side of the neck (fig. 176, A). The intestine is very short, but to compensate for this, the nnicous mem- brane is thrown into a fold, which winds round the intes- tine in close turns from near the |iyloiic orifice of the stom- ach to the anus, and wdiich thus greatly increases its ab- sorliing surface. The most characteristic ex- ani|iles of the Elasmobranch Fishes are the Sharks, Dog- fishes, , and Kays, usu- ally called Plagiostomous Fishes, because the moiith is transverse, and is placed on the under side of the head. In all these types there are five branchial pouches on each side, which open by five dis- tinct slits on the surface of the body. There are also two apertures ("spiracles") on the to]) of the bead, just behind the eyes, which lead by tnbes into the j>hai\ iix, and which correspond with an anterior pair of branchial jiouclies. The Sharks ami Dng-fislies {Si) have jiectoral fins of the ordinarv size and (fig, 176, A), and have the jilaced on the sides of the neck. They have 'p teeth, in .several rows, and they are nearly all and fierce animals. The Shai'ks in ;i. great size. The Port Jackson Sharks (Ci'slrariiui) of th
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
