52 MAMMALIA. 



it lies as a simple azygos pouch, provided internally with small de- 

 pressions, between the umbilicus and the glans penis. 



In many Ruminantia, such as the Sheep, Doe, Elk, and Rein- 

 deer, we frequently find over the hoofs, both in the fore and hind 

 feet, or only in the one set, a membranous pouch of considerable 

 size, beset with follicles, which secrete a fatty odorous substance, 

 which is poured out upon the anterior surface of the hoof above 

 its cleft. 



A most peculiar gland, proba"bly a Poison gland (and in this case 

 it would be, as such, the only example in a mammiferous animal), 

 occurs in the male Ornithorynchus. It is a considerable triangular 

 gland, which lies upon the outer side of the leg. A long excretory 

 duct runs beneath the integument to the inner side of the heel as fal 

 as the astragalus, where it forms a sacculate dilatation at the base of 

 the horny spur, and opens at length by a canal traversing the latter 

 to its apex. 



SEXUAL ORGANS. 



THE sexual organs of the Mammalia and the organs of lactation, 

 which must be here considered also, differ very much from those of 

 the other Vertebrata. They repeat with certain modifications the 

 human type of formation. 



The Ovaries are, as a rule, rounded or oviform bodies, as in Man, 

 in which are imbedded in a more or less dense fibrous stroma the 

 Graafian follicles. In each of the latter there lies one small ovule 

 (very rarely two), scarcely visible by the naked eye, which includes 

 a germinal vesicle with a single germinal spot. If the stroma is in 

 small quantity, the follicles frequently appear pedunculated, and thus 

 the ovarium obtains a more clustered appearance, as is the case in the 

 Mole and Ornithorynchus. 



The Fallopian tubes or Oviducts usually commence, as in Man, 

 by a free opening into the abdominal cavity, and are usually sur- 

 rounded by a puckered border of folds, forming what are called the 

 fimbriae. In many Carnivora, e. g. Canis, Felis, Phocha, Mustela, 

 Lutra, the peritoneal covering of the oviducts is continued to the 

 ovary, which it loosely invests, after the manner of the testicle, with 

 a kind of tunica vaginalis. In some animals, as the Dog and Cat, 

 a small opening remains in this sac, communicating with the abdom- 

 inal cavity ; in others the sac is completely closed, and in these last, 



