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MANUAL OF ELEMENTARY ZOOLOGY 



that its members lay large, yolky eggs with shells, like those 

 of reptiles and birds. Their temperature varies a good 

 deal, and averages little above 25° C, whereas that of other 

 mammals is pretty constant at about 38 C. 1 Their urinary, 

 genital, and anal openings discharge into a common cloaca, 

 and their shoulder girdle has well-developed precoracoids 

 and coracoids which meet the breastbone. The Duckmole 

 (Ornithorhynchus) is an example of this group. It is a 



Fig. 335. — The shoulder girdle and breastbone of a duckmole. 



cL, Clavicle ; cor., coracoid ; g-.c, glenoid cavity ; i.cl., interclavicle ; 

 p.c, precoracoid ; r. t ribs ; sc, scapula ; St., sternebrae. 



small, aquatic animal with webbed forefeet and a horny 

 bill, which lives in burrows in river banks in Australia. 

 All other mammals have minute eggs, which are not laid, 

 but undergo a great part of their development within the 

 body of the mother, from which they receive nourish- 

 ment. They have no cloaca or precoracoids, and the 

 coracoids are small projections of the scapula. Among 

 them the Pouched Mammals, Metatheria, or Marsupialia, 



1 The average temperature of man is about a degree lower than that 

 of most mammals. 



