298 F. H. EDGEWORTH. 



On Furbrixgek's Theory of the Skull. 



It is of interest to inquire whether the above suggestions 

 as to the phylogeny of various groups of Vertebrates receive 

 any support from tlie morphology of the skull. 



According to Ftirbringer's theory the portion of the cranium 

 in front of the exit of the vagus is the original cranium — the 

 pala^oci-anium. The neocranium has lieen formed by the 

 addition of spinal skeletal elements, which originally were 

 free. This took place in several stages ; ill the first a proto- 

 metamer neocranium is formed — present in Selachii and 

 Amphibia. The union of further additional elements l)rings 

 about the auximetamer condition of the neocranium, found in 

 higher fislies and Amniota. 



The added spinal nerves — spino-occipital nerves — can be 

 divided into two categories, the " occipital," brought in with 

 the protometamer neocranium, and the " occipito-spinal," 

 additionally added with the auximetamer neocranium. The 

 varying number of spino-occipital nerves is due to the varying 

 position of the cranio-vei'tebral junction. 



The assimilated occipital nerves are indicated by the 

 terminal letters of the alphabet, the assimilated occipito- 

 spinal nerves by the initial letters. Their corresponding 

 myotomes are given corresponding (larger) letters. By this 

 method it is possible to express either or both of two possi- 

 bilities — the reduction of more anterior or the addition of 

 more posterior nerves. 



The following table, which is taken mostly from Graupp, 

 shows the results of the investigation of various vertebrates, 

 and a column has been added showing the number of 

 myotomes taking part in the formation of the hypo- 

 branchial muscles. 



A spinal segment is typically indicated by a somite or 

 myotome, anterior nerve root, and posterior nerve root. The 

 researches of Furbringer and other observers have shown that 

 as segments are assimilated their nerve roots tend either not 



