1018 



secondarily epi branchial myotonnes, as we can do so clearly in 

 Petromyzon, and taking them all for secondarily epibranchial and 

 of post-branchial origin, arrived at erroneous conclusions. No "heiszer 

 Kampf der Theile" (Fkorikp, 1901, p. 372): peace and rest are 

 reigning in the occipital region. 



3. Fürbkingkr's (1897) conception of the metanieric structure of 

 the Amphibian cranium, and as a consequence also that concerning 

 the skull of Amniotes, is false. The Amphibian skull does not, as 

 FüKBRiNGER (1. c. p. 485) assumcs a priori, contain as many segments 

 as that of Selachians, but less (Skwertzoff, 1897, p. 410). The single 

 occipital nerve which sometimes may be observed in early stages 

 of development of Amphibians, was accounted for above. It is not 

 to be considered as a last remnant of more occipital nerves {x, y, z) 

 corresponding to those of Selachians, it is accordingly not z, but r. 



The occipital hypoglossus roots of Amniotes do not owe their 

 presence to a second annexation of fiee segments, but correspond 

 to those of Selachians, not to the anterior free roots of the latter. 

 The oldest conception (GKCiKNBAUR, 1871, p. 532j once more proves 

 to be the right one here. Occipito-spinal nerves {a, b, c, etc. after 

 FüRBRiNGER) (lo uot cxist, at least not in Amniotes. Only if with 

 FüRBRiNGER (1. c. p. 3G2) oue designates the last occipital nerve of 

 Acantliias as a, we ought to do so equally with Amniotes. The 

 "ganglion hypoglossi", discovered by Froriep (1882) in the last head 

 segment of the sheep, evidently corresponds to the ganglion in the 

 last head segment of Acanthia.^. The sharp distinction between 

 proto- and auximetameric neocranium must be left out, at any rate 

 the Amphibians have no protometameric neocranium (which is of 

 equal length to that of Selachians), nor have the Amniotes an 

 auximetameric neocranium (longer than that of Selachians) in Für- 

 bringer's sense. Only in Notidanidae and Chondrostei could one 

 speak of an auximetameric neocranium and of occipito-spinal nerves. 



Surely the hypoglossus has originall}' nothing to do with the 

 vagus, as Petromyzon teaches us ; that in higher Chordates it ap- 

 proaches the latter so closely that we may partly designate them 

 with Gegenbaur as ventral vagus roots, (i.e. of the partially poly- 

 meric vago-accessorius, better still of the accessorius which originates 

 in closest connection to the anterior, rudimentary ganglia behind the 

 vagus and in Selachians has not yet separated from the latter), is 

 not to be accounted for by a forward movement of the myotomes 

 and ventral roots themselves, but by a displacement of the 

 "segmental hypoglossus level" in forward direction 

 as a consequence of the decrease of the number of 



