90 ALUS. [Vol. II. 



segments of Amia ; and that the nerves related to these seg- 

 ments in the two fishes, that is, the first five postvagal nerves, 

 agree even more closely with each other in their general periph- 

 eral distribution. The relations of these several nerves and 

 segments to the skull and vertebrae are, on the contrary, totally 

 different in the two fishes ; for the fourth and fifth intermus- 

 cular septa have their respective attachments, in Scomber, to 

 the first and second free vertebrae, while in Amia they have 

 their attachments to the two occipital arches. This marked 

 difference in the two fishes would find an evident and simple 

 explanation in the assumption that the first two free vertebrae 

 of Scomber were, in Amia, partly incorporated in the occipital 

 part of the skull. But this assumption is directly opposed to 

 Furbringer's general conclusions, according to which it must 

 be assumed that the first two free vertebrae in the two fishes 

 are strictly homologous. Under the first assumption there 

 would be, in the two fishes, a marked accord in the nerves and 

 muscle-segments of the region. Under the second assumption 

 there are marked differences to be explained and accounted for. 

 In Scomber, for instance, the fourth muscle-segment lies 

 between the hind end of the skull and the first free vertebra, 

 and it is innervated by the posterior one of the three nerves 

 that issue through the foramina in the occipitale laterale. The 

 next, or fifth, muscle-segment lies between the first and second 

 vertebrae, and is innervated by the first free spinal nerve, the 

 roots of that nerve traversing foramina that lie in the first 

 vertebra close to, but posterior to, the intermuscular septum 

 that has its attachment to that vertebra. In Amia the first 

 free spinal nerve innervates the muscle-segment that lies 

 between the hind end of the skull and the first free vertebra. 

 The homologue, in Scomber, of the first free spinal nerve of 

 Amia is, accordingly, in so far as the morphological relations of 

 the nerves to the skull and vertebrae are concerned, the last 

 spino-occipital nerve, and not the first free spinal one. The 

 insufficiency of Furbringer's definitions is thus at once evident, 

 for an examination of the skull alone in the two fishes would 

 not in any way indicate that the last spino-occipitai nerve was 

 not, in each, similarly related to the last occipital vertebra. 



