28 Macteay Memoriat Vouume. 
Probably in the earliest forms in which lungs were developed as respiratory struc- 
tures the mode of life was very similar to that of Ceratodus. The animal lived in 
water and at first at any rate and possibly for long the lungs were accessory organs 
used normally together with the branchie. They were functional throughout life 
and in the early life of the tadpole of Rana we have reproduced, so far as the 
respiratory system is concerned, a condition which is normal to Ceratodus through- 
out its whole life. 
The development in Ceratodus of a single instead of a double lung as in 
Protopterus has brought about certain differences in these two forms in the 
pulmonary arteries. Both forms, however, have two—a left and a right one— 
present® and in both the left passes to the ventral surface, and the right to the 
dorsal surface. 
In the arteries also it may be noted as an interesting point that there is present 
a vessel passing forwards from the ventral end of the efferent artery of the first 
branchial arch which is evidently directly comparable to the lingual artery of 
Amphibia, which, as previously mentioned, Marshall and Bles have shown to arise 
from the same vessel in Rana lemporaria. 
In certain respects, however, the arterial system shows close relationship to 
that of Elasmobranchs. 
The most important of these are, (1) the presence of two efferent arteries in 
each arch—an anterior and a posterior one. This is a very characteristic elasmo- 
branch feature. Apparently in the dévelopment of Rana there is no trace of 
anything corresponding to the posterior of the two efferent arteries, the single one 
of the latter forms being the homologue of the larger and, in the Elasmobranchs, 
earlier developed anterior vessel. Ceratodus appears, however, to be more primitive 
than the adult Elasmobranch since throughout life the efferent vessels of the same 
arch unite to form an epibranchial, a condition which only obtains in the latter forms 
during early embryonic stages. 
(2) The origin and distribution of the carotid arteries. Whilst in Elasmo- 
branchs, Ceratodus, and Amphibia a carotid vessel arises from what may be 
regarded as the forward prolongation of the dorsal aorta on each side, in the two 
former it is a branch connected ultimately with the vessel in the hyoidean arch which 
* Zur Anatomie und Physiologie von Protopterus annectens. Berichte der Nat. Gesell. Freiburg, 1888. 
W.N. Parker. 1 am unfortunately unable to refer to Hyrtl’s paper on Lepidosiren paradoxa, but according to Professor 
W. N. Parker the latter has shown that two pulmonary arteries are present in this form. A curious mistake may here 
be noted in the English translation of Wiedersheim’s ‘‘ Comparative Anatomy of Vertebrates.” On page 281] it is stated, 
“in Ceratodus the lung is supplied with blood from the coeliac artery.” This mistake has evidently been copied from 
Giinther’s original paper and does not occur in the original German work, nor does it correspond to the figure on page 280 
of the English translation. 
