DE. A. GUNTHEE’S DESCRIPTION OE CEEATODTTS. 
541 
verse septa ; there are twenty-eight on the left side, and thirty-three on the right, the 
latter half extending more forwards than the former. The foremost and hindmost com- 
partments are much shallower than the others, which have a cubic shape, being about 
half an inch wide, and one third of an inch long and deep. The septa separating the 
compartments are imperforate membranes, so that each compartment can be separately 
tilled with fluid, only the side towards the median line of the lung being open. The 
bottom of these compartments is again divided into a number of larger and smaller 
cells by reticulated septa, which are very irregularly disposed. A very dense network of 
the branches of the pulmonal arteries and vein extends all over the surface of the lung, 
and its principal and secondary septa ; the terminal branches of both arteries and vein are 
rather wide, and can be injected with great facility. 
The principal arterial vessels of the lung are on the dorsal side of the organ, running 
along, and very close to, each side of the aorta ; that on the right side is much stronger 
than the left, and can be injected from the arteria cceliaca. There is no direct arterial 
communication between the lung and the arcus aortee, as in Lejndosiren. The two 
arteries mentioned distribute blood through the entire length of the lung, to its posterior 
end ; their ramifications are confined to the inner surface of the organ, and not visible 
externally. 
On the median line of the ventral side of the lung, opposite to the dorsal arteries, are 
two vessels (f and f'), of the arterial nature of which I could not satisfactorily convince 
myself. Their ramifications are also spread over the inner surface and collected into 
the two stems running along each side of the smooth band in the median line of the 
lung, the left stem being wider than the right. After their union near the anterior 
end of the lung, the single vessel turns off towards the right side of the oesophagus, 
which it then crosses from the right towards the left, at a short distance above the 
glottis. Arrived on the left side, it descends again, as far as the basal portion of the 
first rib, and splits up (at g) into three very small branches, which I could not follow 
further. Great care was taken in ascertaining the very singular termination of this 
vessel, which I expected to take its origin from the left arteria sub clavia ; but no such 
connexion could be discovered. 
The ramifications of the venae pulmonales ( e and d) are more visible on the external 
surface of the lung than on the internal ; they are collected into a common branch, 
running near to the outer margin of the ventral surface of each half of the long ; the 
left branch is stronger than the right ; both unite near the anterior end, and on the right 
side of the lung; its passage through the diaphragm and separate entrance into the 
atrium have been noticed above in the description of the heart. 
At the beginning of this paper (p. 514) statements have been referred to, from which 
it would appear that Ceratodus is in the habit of going on land, or at least on mud-flats ; 
and this assertion seems to be borne out by the fact that it is provided with a true lung. 
On the other hand, we must recollect that a similar belief was entertained with regard 
