A FISH BRAIN FROM THE COAL MEASURES 141 
with great accuracy and certainty. The parts that are preserved 
give us certain fixed points that enable us to determine the size and 
location of the brain with a reasonable degree of certainty. The 
general form of the brain and the direction of the principal nerves 
may be inferred from the size and location of the principal sense organs 
and viscera. These fixed points are as follows: 
(1) A small vertical ethmoidal plate (figs. 1 and 2, e) lies between the 
olfactory openings and extends almost to the inner shelf of the rostral 
plate. The forebrain probably extended well up to this plate but not 
beyond it. 
(2) The two small olfactory openings just in front of the lateral 
eyes, indicate the presence of paired olfactory organs, of small size, 
lying on either side of the ethmoidal plate, in the chamber formed by 
the inner and outer shelves of the rostral plate (figs. 1 and 2, ol.o). 
(3) A deep, clean-cut, conical cavity on the inner surface (of the) 
middle occular plate, and a pronounced lens-like swelling on its outer 
surface indicates the presence of an exceptionally large and well-de- 
veloped pineal eye (figs. 1 and 2, p.e.). Caudad to it are two other pit- 
like depressions on the inner surface of-the semilunar post-occular 
plate, indicating the presence of two other similar organs (figs. 1 and 2, 
pew): 
(4) Two small pores in the occipital plates mark the location of 
the openings to the endolymphatic ducts (figs. land 2, d.e.) and indicate 
the presence of underlying auditory vesicles (figs. 1 and 2, auw.). 
(5) In sagittal sections, a blackened band (fig. 2, b.pl.) extending 
backwards from the inner shelf of the rostral plate probably represents 
the floor of a cartilaginous endocranium. 
(6) The stomach and gills are located in the large posterior chamber. 
(7) A pronounced hinge joint marks the line separating the branchial 
and visceral region from the head proper, in which the brain, jaws and 
principal sense organs are located. 
(8) Two median bony processes extend inwards from the roofng 
plates of the branchial region that served for the support of the muscles 
and tough connective tissue. The spinal cord probably lies just be- 
low the blackened remnants of these tissues. No trace of a notochord 
or vertebral column could be found. 
All these characters enable us to locate the brain within the chamber 
between the floor of the endocranium and the occular plates, and 
indicates that the brain had a form and location like the one shown in 
the restoration (fig. 1). The location of the median and lateral eyes 
and the olfactory organs, in a compact group, on the dorsal surface is 
suggestive of the cyclostomes. 
The anatomy of this form (Bothriolepis) with suggestions as 
to its phylogenetic significance are given fully in Professor Pat- 
ten’s work’ to which reference has been made for the condition 
§ The evolution of the vertebrates and their kin. Philadelphia, 1912. 
