CHAPTER Vm. 



THE CLASSIFICATION AND ORGANIZATION OF THE MAMMALIA. 



The class Mammalia is divisible into the following groups : 



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

 Eternum. 



The ureters and the genital ducts open into a cloaca, into which 



the urinary bladder has a separate opening. 

 The penis is traversed by a 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 a ure- 

 thra or vagiua. 

 The cystic urethra 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 an allantoic placenta. The vagina is double. 



II. DlDELPHIA. 



2. ifarmpiaUa. 



B. The embryo has an allantoic placenta. The vagina is single. 



III. MON ODELPHI A.. * 



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



3. Edentata. 



h. Median incisor teeth are almost always developed in one or 

 both jaws. 



♦ The manner in which the MonodelpTiia are here subdivided must be re- 

 garded as merely provisional. 



