ORIGIN AND STR UCTURE OF THE HEAD 113 



much simplified. The antagonism between head and 

 trunk, the invasion of the trunk-myotomes into the occipital 

 region, the "stetiges Vorrucken" of the former (FuRBRlNGER, 

 1897, p. 440), the struggle between the neural crest of the head 

 and that of the trunk, the hand to hand contest between the 

 dorsal and ventral roots of the two enemy regions, all painted 

 to us by Froriep (1901, p. 372) as the "heiszen Kampf 

 der Theile', fade away like a fata morgana: peace and 

 rest appear to reign in the occipital region. 



Hypoglossus oj Amnioies. — The question has been partly 

 answered already as to whether in the case of the hypoglos- 

 sus in Amniotes, the "occipito-spinal" nerves of FuRBRlNGER, 

 there is more reason to assume all these complicated displace- 

 ments than in that of the occipital roots in Elasmobranchs, to 

 which the hypoglossus shows such an undeniable resem- 

 blance. Is the distinction between a protometameric and 

 an auximetameric neocranium a firmly founded one? These 

 terms, introduced by FuRBRlNGER, are found in every 

 text-book, every student knows them (and if he does not, 

 he will have a bad chance in his examination) and their 

 general acceptance seems to allow hardly any doubt as 

 to the correctness of this distinction. According to it, three 

 of the anterior spinal nerves of Elasmobranchs and Amphi- 

 bians, 1, 2, and 3 — at least their ventral roots, the dorsal 

 ones having again atrophied — have been incorporated in 

 Amniotes as a, b and c (occipito-spinal nerves) into the 

 cranium to which accordingly once more a corresponding 

 number of vertebrae has been assimilated. These three 

 ventral roots form the hypoglossus which, together with 

 the anterior spinal nerves, innervates the tongue-musculature 

 which is to be derived from the hypobranchial muscles of 

 Elasmobranchs. At exactly the same place where in the 

 latter the "ventral vagus roots" are found, that- is right 

 under the vagus and its derivative the accessorius, which, 

 as shown e. g. by VAN Bemmelen (1889), arises in close 

 connection to the rudimentary dorsal ganglia behind the 

 vagus, we find in Amniotes the hypoglossus-roots. Once 

 more, according to FuRBRlNGER, we must assume such an 

 improbable moving of ventral roots (and corresponding 

 myotomes) in forward direction over a distance of several 

 segments till they have arrived right under the dorsal 

 roots of segments far in front of them, a displacement for 

 which not a single reason can be given. On the contrary, 



