The prostate is met with in its most simple form in mar supials, in which it is a mere thickening of the mucous mem brane of the urethra ; in the sheep it forms a bilateral elongated mass of gland tissue lying behind the urethra and surrounded by a well-developed layer of striped muscle. In the sloth it is said to be altogether absent, while in many of the insectivores and rodents it consists of many lobes which usually show a bilateral arrangement. The vesiculae seminales are usually present in higher mammals, and sometimes, as in the hedgehog, are very large, though they are absent in the Carnivora. Cowper's glands are usually present and functional throughout life. The uterus masculinus is also usually present, but there is grave doubt whether the large organ called by this name in the rabbit should not rather be regarded as homologous with part of the vesiculae seminales. The penis shows many diversities of arrangement ; above the marsupials its two crura obtain an attachment to the ischium. In many mammals it is quite hidden by the skin in the flaccid condition, and its external orifice may range from the perineum in the marsupials to the middle of the ventral wall of the abdomen in the ruminants. In the Marsupialia, Rodentia,
Chiroptera, Carnivora and some Primates an os penis is developed in connection with the corpora cavernosa.
The clitoris is present in all mammals; sometimes, as in the female hyena, it is very large, and at others, as in the lemur, it is perforated by the urethra.
See Quain's Anatomy; Gray's Anatomy; Cunningham's Text-Book of Anatomy; Macalister's Anatomy; Oppel's Lehrbuch der vergleich. mikroskop. Anatomie der Wirbelthiere, Bd. iv. (Jena, 19°4) ; Gegen baur's Vergleich. Anat. der Wirbelthiere; Wiedersheim's Comparative Anatomy of Vertebrates, translated by W. N. Parker (London, 19°7) ; E. R. Bundy, Textbook of Anatomy and Physiology (5th ed., 1923) ; F. H. A. Marshall, Introduction to Sexual Physiology (1928) and The Physiology of Reproduction (2nd ed., 1922) ; J. Hammond, Reproduc tion in the Rabbit (5925) ; Buchanan's Manual of Anatomy (5th ed., 1925) ; W. H. Howell, Textbook of Physiology (1927). (F. G. P.)