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THIS IS A MAMMAL" 



Featured Exhibit for June 



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Philip Hershkovitz 

 Curator, Mammals 



\m% is a mammal" is the title of 

 fune's Exhibit-of-the-Month in 

 Stanley Field Hall. The display is the 

 first completed in a series being prepared 

 for a redesigned Hall of Mammals. 



The exhibit uses actual specimens, 

 models, drawings, and text to illustrate 

 the distinctive anatomical characters of 

 mammals and to show how mammals 

 differ from all other animals. Some of 

 the outstanding mammalian features are 

 the nourishment of young with milk pro- 

 duced by the mother, the facial muscles 

 developed primarily for suckling, the 

 body covering of hair, the four-cham- 

 bered heart with the main artery on the 

 left side, and the muscular diaphragm 

 which separates the lungs from the gen- 

 eral body cavity. 



Among the most important characters 

 of mammals, certainly from the point of 

 view of zoologists concerned with the 

 earliest creatures of the kind, are those 

 found in the hard parts, which may be 

 preserved as fossils. The differences be- 

 tween living mammals and other living 

 animals are many and clear. The dis- 

 tinction between mammals and the ex- 

 tinct mammal-like reptiles from which 

 they evolved more than 160 million 

 yeas ago rests primarily on the structure 

 of the lower jaw and the way it hinges 

 on the skull. 



The lower jaw of a mammal consists of 

 a single bone, the dentary. The reptilian 

 lower jaw is made up of the dentary and 

 a number of other bones including the 

 articular, which hinges with the quad- 

 rate of the upper jaw. In mammals the 

 dentary itself hinges directly on a bone 

 of the brain case, the squamosal. 



Somewhere along the evolutionary 

 line from reptiles to mammals these two 

 little hinge bones of the reptilian jaw 

 found a new place and function. Still 

 jointed, the reptilian articular and quad- 

 rate bones moved into the middle ear 

 and, joining the stapes, became the mal- 

 (Continued on page 8) 



Above : The chief internal organs of a typical mammal. 

 The model, sculptured in plexiglass that reveals the in- 

 ternal parts in color, shows the normal position of the 

 brain, heart, lungs, and other organs which are displayed 

 separately on the exhibition panel. 



Left: Skin glands of mammals. A greatly magnified 

 section of skin shows hairs, the oil glands around their 

 base, and the sweat glands which help maintain an even 

 body temperature. 



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