Spencer—Zhe Blood Vessels of Ceratodus. 29 
carries arterial blood to the brain and gives rise to the cerebral arteries. There are 
certain differences in the origin of this in Elasmobranchs and Ceratodus, already 
noticed and due to the presence in the former and absence in the latter of a 
pseudobranch ; but whilst the carotid system of these forms is undoubtedly closely 
similar the vessels in both differ considerably from those of Amphibia with which it 
is not possible at present to exactly homologize them. 
(3) The presence in Ceratodus of an intra-intestinal artery associated with the 
development, as in Elasmobranchs, of a spiral fold in the intestine. 
(4) The presence in Ceratodus, as in Elasmobranchs (Mustelus), of anterior 
spermatic and oviducal arteries which pass off from the dorsal aorta not far behind 
the entrance of the last pair of epibranchial arteries. 
B. The veins. 
In the veins even still more notably than in the arteries we find a remarkable 
mixture of piscine and amphibian types and with this is associated a lack of 
symmetry on the two sides of the body. 
So far as the cardinal system is concerned, the vessels representing the anterior 
cardinal—superior and inferior jugular veins—are closely similar to those of Elasmo- 
branchs and are characterised by the presence of large sinuses and of anastomotic 
branches—a fact to which Prof. Parker has drawn attention in Mustelus.* In fact, 
it may be said that, so far as the vessels, both veins and arteries of the head region 
are concerned, Ceratodus is typically piscine. 
Again, in the presence of a very distinct lateral cutaneous vein which has 
posterior connections with the caudal vein and opens anteriorly into the subscapular 
sinus, whence a large subscapular vein runs down to the Ductus Cuvieri on each 
side, we see a point of nearly precise agreement with Mustelus. On the other hand, 
neither dorsal nor ventral cutaneous branches appear to be present in Ceratodus. 
A further strong point of agreement is the presence of a well-developed intra- 
intestinal vein in connection, as in Elasmobranchs, with the spiral fold. This vessel 
has now been shown to be present in Elasmobranchs, Holocephali (Callorhynchus), 
and Dipnoi (Ceratodus). 
Whilst the above veins reveal piscine affinities, there are others which show that 
Ceratodus has developed to a certain extent along lines at all events parallel to those 
of the Amphibia. This is shown in the development of (1) the inferior vena cava 
system and (2) the anterior abdominal system to which attention may now be drawn. 
* Loc. cit. p. 721. 
