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and the posterior halves of the rami are closely adherent to the fascia of the external oblique in the middle line, and lie between the inner edges of the two recti. Finally, the fibres of the transversus (fig. 13, Trs.) are inserted into the outer edges of the rami, and the fascia which unites these appears to belong to the transversus.
On comparing the recti and the muscles A, B, C, with those of Or. nithorhynchus and Echidna, a great apparent difference manifests itself. For the very thin recti of the Monotremes take their origin from the pubis along a line which extends from the tubercle to close to the symphysis, and pass forwards, dorsad of the marsupial bones and the pyramidales, which thus lie altogether in front of thein and are, by them, largely separated from the fascia transversalis. Nevertheless, it will be observed that the origin of the muscle B nearly corresponds with that of the rectus in Ornithorynchus ; and I am disposed to think that, in this animal, the rectus, at least in its posterior moiety, is represented by the homologue of this muscle, which has extended laterally over the dorsal face of the enormously enlarged homologues of the rami of the ypsiloid cartilage.
However this may be, it must be recollected that it is only the extreme ends of the rami which lie dorsad of the recti, and that, in the rest of its extent, the epipubis of Salamandra is firmly fixed to the fascia of the external oblique, which forms the front wall of the sheath of the rectus. The homology of the epipubis with the marsupial bones is determined by the essential identity of the relations of the two to the tendons of the external oblique muscles.
It seems to me that, in such a pelvis as that of Salamandra, we have an adequate representation of the type from which all the different modifications which we find in the higher Vertebrata may have taken their origin.
In the lizards and the Chelonia the iliac and obturator axes have inclined forwards, and the epipubes have been reduced to such rudiments, as have been described in chameleons and in some tortoises.*
In the crocodiles, with the same general pelvic characters, the cotyloid end of the pubis retains its imperfectly ossified condition, while the epibubes represent the vastly enlarged rami of the salamandrine epipubis.
In the Ornithoscelida and in birds, the ilia elongate, but it is the modification of the pubes and ischia which is the most characteristic feature of the pelvis, and the epipubis vanishes.
In the Pterosauria and in the Dicynodonts, the salamandrine nondevelopment of an obturator fontanelle persists; and, in the former, the sessile rami of the epipubis appear to be represented by the so-called marsupial bones.
* Hoffmann, “Beiträge zur Kenntniss des Beckens der Amphibien und Reptilien,” “Nied. Archiv für Zoologie,” Bd. 3, p. 143, 1876.
Unless the like should prove to be the case in the Dicynodonts, it is in the Mammalia alone that the subsacral portion of the ilium elongates backwards, carrying with it the pubis and the ischium, between which a large rounded obturator fontanelle is developed.
These facts appear to me to point to the conclusion that the Mammalia have been connected with the Amphibia by some unknown“ promammalian " group, and not by any of the known forms of Sauropsida ; and there is other evidence which tends in the same direction.
Thus, the Amphibia are the only air-breathing Vertebrata which, like Mammals, have a dicondylian skull. It is only in them that the articular element of the mandibular arch remains cartilaginous; while the quadrate ossification is small, and the squamosal extends down over it to the osseous elements of the mandible; thus affording an easy transition to the mammalian condition of these parts.
The pectoral arch of the Monotremes is as much amphibian as it is sauropsidan; the carpus and the tarsus of all Sauropsida, except the Chelonia, are modified away from the Urodele type, while those of the Mammal are directly reducible to it; and it is perhaps worth notice, that the calcar of the frogs is, in some respects, comparable with the spur
of the Monotremes. Finally, the fact that, in all Sauropsida, it is a right aortic arch which is the main conduit of arterial blood leaving the heart, while, in Mammals, it is a left aortic arch which performs this office, is a great stumbling-block in the way of the derivation of the Mammalia from any of the Sauropsida. But, if we suppose the earliest forms of both the Mammalia and the Sauropsida to have had a common Amphibian origin, there is no difficulty in the supposition that, from the first, it was a left aortic arch in the one series, and the corresponding right aortic arch in the other, which became the predominant feeder of the arterial system.
The discovery of the intermediate links between Reptilia and Aves, among extinct forms of life, gives every ground for hoping that, before long, the transition between the lowest Mammalia at present known and the simpler Vertebrata may be similarly traced. The preceding remarks are intended to direct attention to the indications of the characters of these promammalian Vertebrata, wbich the evidence at present forthcoming seems to me to suggest.
In the relatively large size of the brain, and in the absence of teeth, the only existing representatives of the Ornithodelphia present characters which suggest that they are much modified members of
On comparing the brain of Echidna, for example, with that of many Marsupialia and Insectivora, its relative magnitude is remarkable: and, in view of the evidence which is now accumu. lating, that the brain increases in size in the later members of the same series of Mammalia, one may surmise that Echidna is the last
term of a series of smaller-brained Ornithodelphia. Among the higher Vertebrata, I think that there is strong reason to believe that edentu. lous animals are always modifications of toothed forms.
EXPLANATION OF PLATE 8.
Figs. 1 to 9. The left half of the pubic arch in Salamandra (fig. 1), Iguana
(fig. 2), Crocodilus (fig. 3), Ornithorhynchus (fig. 4), Echidna (fig. 5), Lepus (fig. 6), Compsognathus (fig. 7), Laosaurus (fig. 8), and Apteryx (fig. 9). The letters have the same signification throughout. II. ilium, Pb. pubis, Is. ischium, Ep.p.epipubis, S. a. sacral axis, Ip. a. ilio-pectineal axis, Ob. a. obturator axis, Il. a. iliac axis, Sy. p., Sy. I., indicate the extent to which the pubes and the ischia unite respectively in their ventral symphyses ; p. p. pectineal process, t. p. tuberosity or spine of the pubis, m. p. metischial process or tuberosity of the ischium, Cl. os cloacæ
in Iguana. Figs. 10, 11. Dorsal and ventral views of the ventral half of the pelvis of Salamandra
maculosa (x4). The letters as before, except Epp. Epp.?, right and left rami of the epipubis or ypsiloid cartilage, Ob. n. foramen of the obturator perve, s. trace of a suture between the ischium and the pubis on the right
side, Ac. acetabulum. Fig. 12. Ventral aspect of the pelvis of a small Crocodilus acutus and the hinder
most abdominal false ribs, of the natural size. The obturator nerve (Ob. n.) perforates the aponeurosis, which fills up the rhomboidal space between the ischia and the pubes, on the inner side of the pubis. Sy. p. l.
the ligamentous union of the pubes. Fig. 13. Dorsal aspect of the epipubis and the muscles connected with it in
Salamandra maculosa. On the left side, the transversalis and the
muscle C. are removed. Fig. 15. The same, all the muscles but the external oblique being removed. Fig. 14. The epipubis and the adjacent muscles in Ornithorhynchus. R. rectus abdominus, Py. pyramidalis, 0. e. obliquus externus, Trs, transversus,
l. a. linea alba, f. fascia, extending between the two rami of the epipubis in Salamandra, P.1. the representatire of Poupart's ligament, i. r. inguinal ring, A. B. C. muscles of Salamandra described in the text. A. and C. together appear to be the pubio-marsupial of Dugès : B. is the hebosteoglossus of von Siebold.
March 13, 1879.
THE PRESIDENT in the Chair.
The Presents received were laid on the table, and thanks ordered for them.
The following Papers were read :
I. “ The Influence of Electricity on Colliding Water Drops.” By Lord RAYLEIGH, F.R.S. Received February 27, 1879.
It has been known for many years that electricity has an extraordinary influence upon the behaviour of fine jets of water ascending in a nearly vertical direction. In its normal state a jet resolves itself into drops, which even before passing the summit, and still more after passing it, are scattered through a considerable width.
When a feebly electrified body is brought into its neighbourhood, the jet undergoes a remarkable transformation, and appears to become coherent; but under more powerful electrical action the scattering becomes even greater than at first. The second effect is readily attributed to the mutual repulsion of the electrified drops, but the action of feeble electricity in producing apparent coherence has been a mystery hitherto.
It has been shown by Beetz that the coherence is apparent only, and that the place where the jet breaks into drops is not perceptibly shifted by the electricity. By screening various parts with metallic plates, Beetz further proved that, contrary to the opinion of earlier observers, the seat of sensitiveness is not at the root of the jet where it leaves the orifice, but at the place of resolution into drops. As in Sir W. Thomson's water-dropping apparatus for atmospheric electricity, the drops carry away with them an electric charge, which may be collected by receiving the water in an insulated vessel.
I have lately succeeded in proving that the normal scattering of a nearly vertical jet is due to the rebound of the drops when they come into collision with one another. Such collisions are inevitable in consequence of the different velocities acquired by the drops under the action of the capillary force, as they break away irregularly from the continuous portion of the jet. Even when the resolution is regularised by the action of external vibrations of suitable frequency, as in the beautiful experiments of Savart and Plateau, the drops must still come into contact before they reach the summit of their parabolic path. In the case of a continuous jet the "equation of continuity shows that as the jet loses velocity in ascending, it must increase in section. When the stream consists of drops following the same path in single file, no such increase of section is possible, and then the constancy of the total stream requires a gradual approximation of the drops, which in the case of a nearly vertical direction of motion cannot stop short of actual contact. Regular vibration bas, however, the effect of postponing the collisions and consequent scattering of the drops, and in the case of a direction of motion less nearly vertical may prevent them altogether.
Under moderate electrical influence there is no material change in the resolution into drops, nor in the subsequent motion of the drops up to the moment of collision. The difference begins here. Instead of rebounding after collision, as the unelectrified drops of clean water generally or always do, the electrified drops coalesce, and thus the jet is no longer scattered about. When the electrical influence is more powerful, the repulsion between the drops is sufficient to prevent actual contact, and then of course there is no opportunity for amal. gamation.
These experiments may be repeated with extreme ease and with hardly any apparatus. The diameter of the jet may be about inch, and may be obtained either from a hole in a thin plate or from a drawn-out glass tube. I have generally employed a piece of glass tube fitted at the end with a perforated tin plate, and connected with a tap by india-rubber tubing. The pressure may be such as to cause the jet to rise 18 or 24 inches, or even more. A single passage of a rod of gutta-percha, or of sealing-wax, along the sleeve of the coat is sufficient to produce the effect. The seat of sensitiveness may be investigated by exciting the extreme tip only of a glass rod, which is then held in saccession to the root of the jet and to the place of resolution into drops. An effect is observed in the latter but not in the former position. Care must be taken to use an electrification so feeble as to require close proximity for its operation, otherwise the discrimination of the positions will not be distinct.
The behaviour of the colliding drops becomes apparent under instantaneous illumination. I have employed sparks from an inductorium, whose secondary terminals were connected with the coatings of a Leyden jar. The jet should be situated between the sparks and the eye, and the observation is facilitated by a piece of ground glass held a little beyond the jet, so as to diffuse the light; or the shadow of the jet may be received on the ground glass, which is then held as close as possible on the side towards the observer.
If the jet be supplied from an insulated vessel, the coalescence of colliding drops coutinues for a time after the removal of the influencing body. This is a consequence of the electrification of the vessel. If the electrified body be held for a time pretty close to the jet, and be then gradually withdrawn, a point may be found where the rebound of colliding drops is re-established. A small motion to or from the jet, or a discharge of the vessel by contact of the finger, again induces coalescence.
Although in these experiments the charges on the colliding drops are undoubtedly of the same name, it appeared to me very improbable that the result of contact of two equal drops, situated in the open, could be affected by any strictly equal electrifications. At the same time an opposite opinion makes the phenomena turn upon the very small