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CHAPTER YIII. 



THE CLASSIFICATION AND ORGANIZATION OF THE 

 MAMMALIA. 



The class Mammalia is divisible into tlie following 

 groups : — 



A. There are large and distinct coracoid bones, which articulate 

 with the sternum. 



The ureters and the a;enital ducts open into a cloaca, into 

 which the urinary bladder has a separate opening. 



The penis is traversed by an urethral canal which opens into 

 the cloaca posteriorly, and is not continuous with the cystic 

 urethra. 



There is no vagina. 



The mammary glands have no teats. 



I. Ornithodelphia. 



1. Monotremata. 



B. The coracoid bones are mere processes of the scapula in the adult, 

 and do not articulate with the sternum. 



The ureters open into the bladder; the genital ducts, into an 



urethra or vagina. 

 The cystic ui'ethra is continuous with the urethral canal of 



the penis. 

 There is a single or a double vagina. 

 The mammary glands have teats. 



A. The embryo does not become connected with the 



wall of the uterus by aa allantoic placenta. The 

 vagina is double. 



II. DiupxriiiA. 



2. Marsupialia. 



B. The embryo has an allantoic placenta. The vagina 



is single. 



III. — MON'ODELPHIA.* 



a. Median incisor teeth are never developed in either jaw. 



* The manner in which the 3Ionodelphia are here subdivided must 

 be regarded as merely provisional. 



