The class Mammalia is divisible into the following groups:
- There are large and distinct coracoid bones, which articulate with the
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.
- 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
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.
- The embryo does not become connected with the wall of the
uterus by an allantoic placenta. The vagina is double.
II. - Didelphia.
- 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.)
- Median incisor teeth are never developed in either jaw.
- Median incisor teeth are almost always developed in one or both jaws.
- The uterus develops no decidua (Non-dediduata).
5. Toxodontia.(?) (The placentation of the Toxodontia and Sirenia is unknown.)
- The uterus develops a decidua (Deciduata).
- The placenta is zonary.
- The placenta is discoidal.