JOURNAL OF THE PROCEEDINGS 



LINNEAN SOCIETY OF LONDON. 



On the Characters, Principles of Division, and Primary Groups 

 of the Class Mammalia. By Professor Owen, F.B.S., P.L.S., 

 Superintendent of the Natural History Departments in the 

 British Museum. 



[Bead February 17th and April 21st, 1857.] 



The class Mammalia, the most highly organized of the animal 

 kingdom and that to which we ourselves belong, appears to have 

 been the last class of animals introduced on this planet, and not 

 to have attained plenary development until the tertiary division 

 of geological time. 



Mammals are distinguished, outwardly, by an entire or partial 

 covering of hair, and (with two exceptions) by teats or mammae — 

 whence the name of the class*. All Mammals possess mammary 

 glands, and suckle their young : the embryo or foetus is developed 

 in the womb. Their leading anatomical character is to have 

 lungs, composed of a highly vascular and minutely cellular struc- 

 ture throughout, and suspended freely in a thoracic cavity sepa- 

 rated by a muscular and tendinous septum or diaphragm from the 

 abdomen. 



* From mamma, a pap. The Platypus and Echidna are the only known 

 exceptions to this rule. The Mare is an apparent one, from the pudendal posi- 

 tion of the nipples. The foetal Cetacea show tufts of hair on the muzzle. 



LINN. PROC. ZOOLOGY. 1 



