It may be found that among the Delphinidæ no two genera, or even species, are alike in the minor details of the structure of the uterus, and more especially of the vagina. This much is suggested by records of dissections which have already been made. Though doubtless accurate they are yet not sufficiently explicit to enable an exact comparison to be made between the different species, whereby we might discover which of these uteri is the more primitive and of the line of evolution which has been followed.
Assuming, then, the accuracy of the published descriptions, it would seem that there exists a fairly wide range of variation in the minor details of the uterine anatomy among the Delphinide.
Thus, in the case of Phocœna phoccena described by Professor Meek (5) the lumen of the anterior end of the vagina was constricted by two great folds, the one rising upwards from the ventral wall, the other hanging down directly behind it from the dorsal vaginal wall, thus forming an 5-shaped lumen. The anterior face of this upstanding ventral fold formed the hinder wall of a “spermathecal recess,” into which the cervix opens. Professor Meek's figure is somewhat diagrammatic, so that it is difficult to say whether the minor foldings on this vaginal wall answer to those seen in dissections at the Royal College of Surgeons.
In the Museum of the Royal College of Surgeons two dissections of the uterus of the Common Porpoise are displayed. One of these (no. 2786) shows a longitudinal section of the vagina. Herein the cervix opens into a wide chamber, the hinder wall of which is constituted by a transverse partition, pierced by a wide aperture leading into a second, similar chamber; but caudad of this the walls are smooth.
In a second specimen (no. 2785) the arrangement appears to be somewhat different.
The cervix, as in the first-named specimen, forms a large, cylindrical, protuberant body, with numerous and fine longitudinal rugosities. It rests an a broad, semicircular, projecting collar, marked by fine longitudinal strk, recalling the collar found in Delphinus. Caudad of this are two broad septa which seem to have been stretched obliquely across the lumen and to have been so fashioned as to give entrance into the chamber enclosing the cervix by means of a failure of the septa to meet the dorso-lateral wall of the left side of the lumen. Three close-set striated ridges lie behind this hindmost septum. The fourth succeeding ridge differs from the rest, inasmuch as it takes an L-shaped form—a broad longitudinal band on the left, and a transverse cylindrical ridge which gradually fades out as it approaches the base of attachment of the second and third septa on the opposite side. There is thus formed a semi-spiral passage from the lower end of the vagina to the chamber into which the cervix opens. This forms an interesting variant on the transverse septum with a perforated centre. There follow behind this a long series of transverse ridges of gradually decreasing width, leaving the rest of the lumen with smooth walls. These transverse ridges answer to the “Os tincœ” of Anderson (1).
According to their labels these two specimens are dissections of the uterus of Phocœna phocéna. Though they were both made by John Hunter, it is just possible that some mistake in identification may have been made, but this is improbable.
In a longitudinal section of the vagina of Tursiops truncatus in the Royal College of Surgeons Museum (no. 2787) the upper segment immediately behind the cervix bears a series of transverse folds projecting into the lumen. The first of these is extensive, pleated, triangular in form, and extending far beyond the cervix. This seems to answer to the thick saucer-shaped fold which I found lying immediately under the cervix in Delphinus delphis. Behind it is a second fold crossing the ventral wall, also pleated. This is succeeded by a third, which completely encircles the lumen, forming a wide transverse septum, the centre of which is perforated to form a circular aperture. A very little modification of this would form the second “or pseudo-cervix” seen in Delphinus. Behind it follow three other transverse folds, more or less completely encircling the lumen, and having a finely pleated surface. Perhaps the duplication of the cervix in Delphinus made the extension of transverse folds behind this unnecessary.
Whether the features described here in Delphinus delphis are relatively fixed, or whether the vaginal cavity will prove to be variable, remains to be seen. Another peculiarity described in this paper calls for further investigation. This concerns the peculiar anchorage of the broad ligament, which suspends the uterus in an obliquely transverse dorso-ventral direction across the body-cavity.
The possibility must not be ignored that this “variability” just referred to in regard to the pleats in the uterus of Phocœna may be due to an error in the identification of the species furnishing the material represented by these two uteri.
That there is justification for this doubt is shown in the case of a paper by Bordas (2) wherein a long and somewhat involved description is given of the uterus of “Delphinus delphis.” At present it would be impossible to determine the source of this uterus, but there is good reason to believe that it is not the uterus of a Common Dolphin. A reference to his very diagrammatic figures alone will suffice to show this.
His descriptions of the vagina, the Fallopian tubes, the ovary, and the infundibulum do not, even remotely, agree with those of Delphinus delphis, but they might be interpreted as an indifferently accurate account of the uterus of Tursiops truncatus, and his figures support this view. This suspicion is strengthened by the fact that John Hunter (4) ascribes the name Delphinus delphis to the Bottle-nosed Dolphin (Tursiops truncatus).
Finally, it would seem that, so far as the available evidence goes, the most primitive type of uterus among the Odontoceti is that of Platanista, described and figured by Anderson (1). Though highly specialized in many ways, yet Platanista displays, especially in regard to the stomach and genital system, what are undoubtedly primitive phases of development which may well represent ancestral stages.