BRAIN AND ORANIAL NERVES OF BDELLOSTOMA DOMBEYI. 139 
primitive, and not degenerative, as has sometimes been 
stated. The older naturalists, deceived by the curious jaw 
formation of the Myxinoids, ranked them as a side branch, 
decidedly separated from other vertebrate forms, but Dr. 
Ayers and Mr. C. M. Jackson, in their paper published in 
1900, solved this puzzle, proving the homology of the 
Myxinoid jaws with those of other gnathostomes, and so 
placing these fishes in the main line of development of the 
gnathostomes. For all these reasons a thorough working 
out of the Myxinoid brain promised to throw much light 
upon that most interesting of problems, the origin and 
development of the vertebrate brain. 
The present paper is a general survey of the ground 
covered by my studies. ‘The following detailed account of 
the gross anatomy of the brain and the distribution of the 
cranial nerves prepares the way for a detailed description of 
the finer anatomy of the several parts of the brain of 
Bdellostoma. The work includes the dissection of Bdello- 
stoma heads preserved in formalin, and the microscopic study 
of sections both of the brain and of the entire head stained 
in hematoxylin or in alum carmine. A discussion of the 
methods used is reserved for a later paper. 
Tue CRANIUM. 
The fishes, from which the brains studied were taken, 
measured from 62 to 64 cm. from the tip of the nose to the 
end of the tail. 
The brain and spinal cord of Bdellostoma lie in a tough 
but flexible capsule of dense fibrous connective tissue. The 
fibres are very thick and tough, some of them being 6°7 yu in 
diameter, and may be either straight or wavy. The capsule 
varies very much in thickness in different parts of its walls, 
these walls being much thinner at the cephalic than at the 
caudal end. 
The general shape of the cranium is that of a flattened 
