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Proceedings of Royal Society of Edinburgh. [sess. 
floor of tlie cavity is formed by the same bone. Each paroccipital 
is responsible for part of the anterior end. The supraoccipital and 
part of the parietal make up the remainder of the end. The inner 
margin is formed by what I have called the neural plate, i.e ., the 
coalesced neural spines. The roof is formed by the dorsal sheathing 
plate. 
It has already been noticed that in the vertebral column, the first 
four vertebrae have coalesced so as to form a simple tube. This 
region of the body, therefore, taking into consideration this tube and 
the dorsal bony plates, exhibits a peculiar rigidity, which must be 
highly serviceable to the fish if my explanation of the unique position 
of the swimming bladder is correct. A similar condition of vertebral 
column is seen in Fistularia (one of the pipe fishes), but here, so far 
as I can find out, the bladder is similar to that seen in the other 
members of the family to which it belongs ; it is, viz., a simple, non- 
muscular bladder, depending in the ordinary way from the dorsum 
of the abdominal cavity. This condition, therefore, although closely 
associated with the swimming bladder in the case of Dactylopterus, 
may not be developed on account of it, or in adaptation to its peculiari- 
ties. In cross section the tube takes much the outline of a cervical 
vertebra without transverse processes. The lower surface is, along 
the median line, formed into a groove, down which passes the dor- 
sal aorta. The eminences on the sides of this groove are hollowed 
out into canals, which, as it were, tunnel through that part of the 
tube to which the bladder muscles are attached, emerging to the 
exterior of the tube before and behind the muscle. In Dactylop- 
terus we have both a body and a head kidney, and the renal veins, 
in passing from the former to the latter, occupy the two canals de- 
scribed above. The kidneys call for treatment in greater detail. 
This will form the subject of another paper. 
