SEXUAL ORGANS. 61 



and uterus, being separated by considerable intervals. In many Ro- 

 dentia, a single rounded placenta is indeed present, but it is divided 

 into several lobes, as occurs occasionally also in Man. In the Apes 

 the placenta consists of two adjacent divisions. In the Hog the whole 

 surface of the choriori performs the function of a placenta. There is 

 no vestige of a placenta in the Marsupiata, which is probably the 

 case also in the Monotremata. 



In Birds and Amphibia, there is found what is called the cloaca, 

 or the termination in a common opening of the urinary and sexual 

 organs. In the Mammalia this structure occurs only in the Mar- 

 supiata and Monotremata. The closest relation of the cloaca to that 

 of Birds is presented by the latter order, where it is provided, as in 

 them, with powerful muscles. 



REFERENCES 



TO 



WORKS UPON THE ANATOMY OF THE MAMMALIA, WHICH MAY BE 

 MOST ADVANTAGEOUSLY CONSULTED IN THE PERUSAL OF THE 

 TEXT. 



General Works upon Comparative Anatomy. 



Cuvier, Lemons d' Anatomic Comparee, 2rde edit. 1835, et seq. 



The treatises upon the Anatomy of the several Orders of Mammalia, in 

 Todd's Cyclopaedia. 



Meckel, System der vergleichenden Anatomic, 1821, translated into 

 French by MM. Riester and Sanson, 1828. 



Carus, Introduction to Comparative Anatomy, translated from the Ger- 

 man by R. T. Gore, 1827. 



Blumenbach, Manual of Comparative Anatomy, translated by W. Law- 

 rence, 1827. 



Gurlt, Handbuch der vergleichenden Anatomic der Haussaiigethiere, 2 

 Aufl. Berlin. 1833. 



Schreber's Saiigethiere, continued by J. A. Wagner, Professor in Mu- 

 nich, 1839. 



Jones, Animal Kingdom, 1841. 



Grant, Outlines of Comparative Anatomy, 1835. 



R. Wagner's Icones Zootomicse, 1841, and Carus and Otto's Erlau- 

 terungstafeln, 1826. 



Tegumentary System. 



Flourens, Anatomic Generale de la Peau, Archives du Museum, torn* 

 3, 1843. 



