. An introduction to zoology : for the use of high schools . the latter the muscular coat is very thick in two places, andthe epithelial lining is converted into horny pads, which servefor the grinding of the food in the granivorous birds. As acompensation for small salivary glands, the pancreas is large,and the length of the intestinal surfiice is increased by two 130 HIGH SCHOOL ZOOLOGY. cceca,, which open into the anterior end of the hirge intestine. CS> 10. Certainly the mostremarkable feature abouttlie respii-atory system ofbirds is the develojimentof air-sacs, which i-eceivetheir air
. An introduction to zoology : for the use of high schools . the latter the muscular coat is very thick in two places, andthe epithelial lining is converted into horny pads, which servefor the grinding of the food in the granivorous birds. As acompensation for small salivary glands, the pancreas is large,and the length of the intestinal surfiice is increased by two 130 HIGH SCHOOL ZOOLOGY. cceca,, which open into the anterior end of the hirge intestine. CS> 10. Certainly the mostremarkable feature abouttlie respii-atory system ofbirds is the develojimentof air-sacs, which i-eceivetheir air from the lungs,and are situated partlyamong the visceia of thebody-cavity, partly be-tween tlie muscles, andunderneath the skin ofI/he body, and finallywithin the bones, dis-placing the marrow inthese. The function ofthese air-sacs is not con-fined to supplementingthe size of the lungs,(although a certain inter-change of gases betweenthe blood and the con-tents of the air-sacs musttake place), but they like-wise serve to render thebody specifically lighter. Fiy. 94—Viscera of the FowL (after Brandt). oe, iBsophagns; ig, crop; tr, trachea; m, muscle;Ui, syrinx ; p, lung^; c, heart; h, liver; dh, hepaticihict; vf,gall-bladder; dch,bile-duct; iiv,]>roveii-triculus; sp, spleen ; v, ;j;i/,zard; d, duodenum ;lia, pancreas; i, small intestine.; toe, its ca-ca ;fo, eiTiJ-follicle burst; o, eiigs ; od, os iduct part-ly slit open containini^ a mature egg, o; cl, clo-aca ; Bz, Bursa Fabrieii. (especially as the bodily temperature is high), and thus moreadapted foi flight. As the birds locomotion involves muchmuscular exertion, both the respiratory and circulatory systemsai-e more perfect than in tlie reptiles, the presence of fourchambers in the heart, allowing the complete separation of theblood which has been returned for aeration, from that which issent out by the heart to the system. 11. In the lower Vertebrates the voice is little developed, HIGH SCHOOL ZOOLOGY. 131 but in the b
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1889
