The omits and fallopian tubes present nothing remarkable in their structure or ar rangement.
Gravid Uterus.— The anatomy of the con tents of the gravid uterus, and the arrange ment of the membranes that enclose the fcetus offer some peculiarities worthy of notice.
The fcetus in utero in the solipeds, is en veloped in the usual uterine membranes, — the amnion, the chorion, and the allantoid ; but the disposition of these envelopes differs remarkably from what exists in the rumi nants, and many other quadrupeds.
The urachus (Ag. 520. a) issues from the umbilicus in company with the umbilical arte ries and vein (b), and, in the ovum represented in the figure, was found at some distance from the umbilical opening to measure about five inches in circumference, beyond which point its diameter gradually diminishes, till it reaches the point at which the amnion spreads out on all sides to envelope the fcetus, where it terminates by the orifice e, and is prolonged to form the allantoid, which encompasses the rest of the cord. On the arrival of the al lantoid at the extremity of the cord, it ex tends itself upon the chorion to which it be comes adherent, lining its internal surface in such a manner, that the two seem to form but a single membrane, the inner surface of which is formed by the allantoid (g), its exterior by the chorion (h).
The size of the umbilical cord gradually enlarges as it approaches the chorion, owing to the progressive dilatation of the vessels composing it as they recede from the umbi licus.
The allantoid in the mare does not form a closed bag, as it does in the ruminants, but lines about half of the interior of the cavity that exists between the amnion and the cho rion. To form an idea of this cavity and of the space occupied by the allantoid, it will be necessary first of all to consider the amnion as a sac, in which the fcetus is enclosed, and the allantoid and the chorion as forming an other sac of larger size, by which the former is enveloped in such a manner, that an inter space is left between the two : this interspace is traversed by the second portion of the umbilical cord as it passes from the former sac towards the latter, and in this course, the cord is enveloped by the allantoid membrane, which subsequently invests all the interior of the second sac formed externally by the chorion.
The aperture of the urachus pours forth a glairy fluid of a reddish colour, which is re ceived into the cavity, the boundaries of which are described above : this fluid has a urinous smell, especially when heated, and moreover contains certain solid bodies, which have been from time immemorial dignified with the name of hipponzanes, and were by the ancients sup posed to be possessed of various mysterious qualities, and magical influences.
The Hippomanes vvas considered, until a very recent period, to be a piece of flesh growing upon the forehead of the nascent foal ; and it was not until Daubenton presented a memoir upon this subject to the Royal Academy of Sciences in Paris *, that its real nature was understood. The hippornanes were then found to be merely masses, of a thick substance, of variable dimensions, tained in the allantoid cavity, which, although they might occasionally during parturition after the laceration of the membranes, become adherent to the head of the fcetus, are, in reality, produced between the _ amnion and the allantoid mem branes.
These bodies are very variable in their size, and frequently several are met with, the dimensions of which vary from the size of a pea to that of a large pear, some of the latter weighing as much as five or six ounces. They are composed of a viscid substance of an olive brown colour, and frequently have irregu. larly shaped cavities in their inte rior; but they present no traces of organization. When cut into they seem to be made up of numerous superposed layers, and exttrnally their surface is covered with float ing filaments : sometimes they are found to be attached by long pe dicles to the walls of the allantoic cavity ; but, whatever their shape, they are evidently merely sedi mentary deposits from the fluid in which they are immersed, and in deed may be formed at pleasure by slowly evaporating the contents of the allantoic sac. These struc tures are indeed by no means pe culiar to the horse, but are fre quently met with in other animals.