Page:The Works of William Harvey (part 1 of 2).djvu/278

 general congeries of smaller ones, in order that it may the more readily find space to grow. Fabricius, therefore, is right when he says, "The yelks which are on the surface of the cluster are larger than those of the middle, which are surrounded as it were by the larger ones. The very smallest of all the ova are situated towards the centre." That is to say, those that grow acquire larger dimensions and become detached from the rest, and as this proceeds, the several yelks, besides their tunica propria, are invested with another from the ovary, which embraces them externally, and connects them with the base whence they spring. This coat is, therefore, entitled the peduncle by Fabricius, and its office is that of a foot-stalk, viz. to supply nourishment to the ovum, in the same way as fruit is nourished through the stalk by which it is connected with the tree. "For this peduncle is a hollow membranous bond of union, extending from the foundation of the cluster [the stroma of the ovary] to the yelk, coming into contact with which, it is dilated and expanded in the same way as the optic nerve in the eye, and covers the vitellus with an external tunic. This perchance was what Aristotle called the, or umbilical appendix, and described as forming a kind of tube. This peduncle includes numerous vessels, which are distributed on all sides around the yelk.

So much is accurately related by Fabricius; but he errs when he says, "This tunic does not surround the entire vitellus, but only extends upon it a little beyond the middle, very much in the manner of an acorn within its cup; whence it comes that the outer portion of the yelk, which is not invested by the membrane in question, presents itself free from vessels, and to appearance naked." The membrane, nevertheless, surrounds the yelk completely; but on the outer aspect it is not very easily distinguished from the tunica propria, both of them being of extreme delicacy. Posteriorly, however, and where the yelk is turned towards the basis of the cluster, the tunic in question does not adhere to the vitellus, neither does it send any vessels to this part, but merely embraces it in the manner of a sac.

Each vitellus receives a distinct tunic from the ovarian basis; whence this is not to be regarded as the common uterus, since