. A manual of zoology. Zoology. Fio. Fig. 348. Fig. 347.âLeft valve of :U(' i^lunihca, inner and outer surfaces. (From Zittel.) The outer surface showing lines of growth : no pallial sinus. Fig. 34K.âRight valve of Mactra .itultnrum, with paUial sinus. (From Ludwig-Leunis.) for both figures: a', anterior; a", posterior adductor scar; c, hinge; (, internal ligamental groove; ?/(, paUial line ;.â >, paUial sinus. When the muscles are relaxed (as always occurs at death) the elastic ligament opens the valves. Tlie heterodout binge is the typical form (fig. 348); ea
. A manual of zoology. Zoology. Fio. Fig. 348. Fig. 347.âLeft valve of :U(' i^lunihca, inner and outer surfaces. (From Zittel.) The outer surface showing lines of growth : no pallial sinus. Fig. 34K.âRight valve of Mactra .itultnrum, with paUial sinus. (From Ludwig-Leunis.) for both figures: a', anterior; a", posterior adductor scar; c, hinge; (, internal ligamental groove; ?/(, paUial line ;.â >, paUial sinus. When the muscles are relaxed (as always occurs at death) the elastic ligament opens the valves. Tlie heterodout binge is the typical form (fig. 348); eacli valve bears a group of teeth near the umbo, those of the left alternating with those of the riglit. Besides these ' cardinal teeth ' there are in front and behind lateral teeth,^ often jiroduced into ridges. The ligament lies behiud the hinge and is usually visible from the outside (external ligament), but is occasionally transferred to the interior (internal ligament, fig. 347). The so- called schizodont and desmodont hinges are modifications of the hetero- dout. Then there are Acophala of apparently primitive character which either lack the liinge (dysodont), or have one composed of numerous teeth in a series symmetrical to the umljo (taxodont), or of two strong teeth like- wise symmetrical to the umbo (isodont). In these cases the ligament is developed in front of as well as behind the umbo, and may be either external or internal. Since the secretion of shell takes jjlace most rapidly at the edge of the mantle, Isoth arc closely uinted, the union hoing strength- ened by small muscles. So the edge of th(^ shell has a different appearance from the rest, this part being marked tf by a pallial line parallel to the margin (fig. 347). In many sjjecies, the Siuu-. 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
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
