413 



b 



crest— paraneuralleiste — fails, as we should naturally expect, to establish 

 any connexion with the central nervous system i). 



Whether this be the case or not it is evident that the meeting 

 place of the cranial and the lateral line system is in the X accessory, 

 that is to say in the spinal accessory, which is clearly a product of the 

 brain type of nerve. The posterior portion of the spinal accessory would 

 appear to have had its origin in the higher vertebrates as a secondary 

 posterior extension of the cranial type into the region of the spinal cord. 



After what has now been set forth a consideration of the neuro- 

 meres and the nerves may be entered upon without taking into account 

 the presence or absence of dorsal ganglia and dorsal roots which belong 

 to the spinal series. 



Seven head somites are represented in the gull, the hinder Umit 

 of the cranium occurring just in front of the nerve of the eighth 

 segment. Froriep has shown that 13 are present at an early stage 

 in the development of Torpedo. These 13 segments I take to re- 

 present myomeres originally associated with the 13 rhombomeres in- 

 dicated in the gull, and their homologues in the vertebrate series. 

 The occurrence of these 13 somites brings us into close proximity to 

 the anterior extremity of the notochord, and I see no reason for 

 doubting that the two preceding neuromeres, mesomeres 1 and 2, were 

 accompanied by myomeres as well. 



Fig. 5. Diagram to indicate the probable origin of the cranial nerves. 



If this be the case then the whole of the notochord region of the 

 skull was originally segmented, and from my reading of the conditions 

 in the gull I conclude that the segments numbered 1572- The probable 

 relation of these to the ganglia I have indicated in Figure 5 and in 

 the following table. 



1) Y. Neumayer, p. 546 — 547; Hertwig's Handbuch, Bd. 2, Teil 3. 



