The Classification and Organization of the Mammalia

1. There are large and distinct coracoid bones, which articulate with the sternum.
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.
2. 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 urethra or vagina.
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.
1. The embryo does not become connected with the wall of the uterus by an allantoic placenta. The vagina is double.
   II. - Didelphia.
   
2. Morsupialia.
2. The embryo has an allantoic placenta. The vagina is single.
   
   III. Monodelphia. (The manner in which the Monodelphia are here subdivided must be regarded as merely provisional.)
   
1. Median incisor teeth are never developed in either jaw.
3. Edentata.
2. Median incisor teeth are almost always developed in one or both jaws.
1. The uterus develops no decidua (Non-dediduata).
   

   4. Ungulata. 5. Toxodontia.(?) (The placentation of the Toxodontia and Sirenia is unknown.) 6. Sirenia.(?) 7. Cetacea.

2. The uterus develops a decidua (Deciduata).
1. The placenta is zonary.
   

   8. Hyrocoidea. 9. Proboscidea. 10. Carnivora.

2. The placenta is discoidal.
   

   11. Rodentia. 12. Insectivora. 13. Cheiroptera. 14. Primates.