Part I.—Venous System.
Hyla aurea is the common frog now found in many parts of New Zealand, where it has become plentiful since its introduction from Australia some thirty years ago. As it is one of the types put down for dissection in the University's biological laboratories, a description of its anatomy, illustrated by original drawings, will, I hope, prove acceptable.
The practical books* used in Australasia to-day all describe, as far as I can ascertain, the European form Rana; and though I have searched through the Transactions and Proceedings of the learned societies of Australasia, with the exception of Miss Sweet's paper† I have found nothing on the above subject. If Hyla aurea corresponded closely in its anatomy to Rana, this absence of literature on the former would not be of much consequence; but in many ways, and especially in the veins, the difference is so marked as to make the description of Rana more or less useless in a dissection of Hyla aurea.
The veins in Hyla aurea not only differ from those of Rana, but they also vary greatly in the different specimens; and in order to obtain as correct a description as possible some fifty frogs have been dissected, besides many notes have been taken from the specimens used in the biology classes.
The description here appended, though not applicable in detail to every specimen, will, I think, be found correct if a number of frogs be dissected and the most general arrangement of the veins be taken.
The following are some of the more common variations:-
1. The arrangement and size of the veins supplying the skin.
2. The size, number, and direction of the smaller branches of the external jugulars.
3. The size and branching of the lingual veins. (Out of fifteen frogs, five had these veins showing well, but they were
[Footnote] * “The Frog,” A. Milnes Marshall, 6th edition; “Anatomy of the Frog,” Ecker (Eng. trans., Haslem). 1889; “Practical Zoology,” Parker and Parker; “Atlas of Zoology,” Howes.
[Footnote] † “Variation of the Spinal Nerves of Hyla aurea,” P.R.S. Vic., vol. ix, new series, p. 264.
much thicker than usual; in six they were about normal; and in four they were almost if not quite invisible.)
4. The size, direction, and division of the external jugulars, which may become very much looped along their courses.
5. The division of the subclavian into its two branches. (Out of fifteen frogs, seven had the division near or at the shoulder, six about half-way between the shoulder and the vena cava, and two near the vena cava.)
6. The number of the renal veins. (These seem to vary between five and seven.)
7. The division of the anterior abdominal vein as it breaks up into the lobes of the liver. (Out of fifteen frogs, five had a large branch running into the left lobe, and the other ten had no large branch, but each lobe was supplied by several smaller branches.)
8. The size of the lumbar veins. (Out of fifteen frogs, twelve had them distinct, and in three they were very small.)
9. The size of the ileo-lumbar veins. (In some specimens they were large and distinct, while in others they were very small and indistinct.)
The lumbar and ileo-lumbar veins are often united by a connecting vein. (Out of fifteen frogs, five had a distinct and good connection, in seven a fair connection, and in three there was no connection at all visible.)