[Campbell Biology Page 956] Campbell Biology 12th Edition
the end of the esophagus, the bolus encounters a sphincter , a ringlike valve of muscle Figure 41.10 . Acting like a drawstring, the sphincter regulates passage
the end of the esophagus, the bolus encounters a sphincter , a ringlike valve of muscle Figure 41.10 . Acting like a drawstring, the sphincter regulates passage