THE SPINAL NERVES. 8l 



the neocraniuni begins. The higher mammals have lost 

 from five to six of the first spinal metameres as compared 

 with the Notidanidae, the hypoglossus nerve correspond- 

 ing probably to the ventral root of the twelfth spinal 

 segment of Myxine. 



In the bony fishes there are, as a rule, no occipital 

 nerves, the first occipito-spinal nerve {a) of the ganoids, 

 etc. , is lost, and the second and third occipital nerves {b 

 and c) are present, usually more or less intimately united 

 with each other and often with the next following, or first 

 true spinal nerve (4 of Fiirbringer's nomenclature, my 

 second spinal). In most of the teleosts examined by Fiir- 

 bringer the ramus cervicalis is formed chiefly from b, with 

 the addition of a variable number of fibres from c. In 

 one case it is formed, however, wholly from b, as in the 

 specimen of Menidia figured. 



It is interesting to note that in Menidia the process of 

 cephalization has gone farther in this respect than in any 

 teleost mentioned by Fiirbringer; for the "occipito- 

 spinal " nerves b and c of those teleosts have here become 

 "occipital" nerves. That is, the corresponding vertebra 

 has been fused with the skull and they therefore emerge 

 through the cranium. This is a phenomenon difficult of 

 explanation in view of the low taxonomic position given 

 to Menidia among the teleosts. It may be a cenogenetic 

 acquisition correlated with the excessive development of 

 the ears and the cranial parts with which they are related. 

 In any case it does not stengthen one's confidence in the 

 spino- occipital nerves as guides to phylogeny. 



This latter conclusion I find is confirmed by Allis' latest 

 paper ('98). From dissections of Scomber made under 

 his direction by Dr. J. Dewitz, he finds a condition of the 

 spino-occipital nerves which conforms neither to Fiir- 

 bringer's account of the teleosts nor to my findings in 

 Menidia, but much more closely to Amia. The spino- 

 occipital nerves a, b and c of Fiirbringer are all present, 

 though their roots, as in Menidia, emerge through the 

 occipitale laterale of the skull and fuse into a single gan- 

 glionic complex. From this and other cases cited by Allis 



