MOTOR NUCLEI IN PHYLOGENY ona 
hyoideus) to be found even in the embryo of this form. In 
Amia according to Allis (1) this muscle, which is subject to great 
variation in different individuals, ‘‘undoubtedly represents a 
muscle in the process of deterioration and disappearance.”’ 
This author demonstrated that the nerve supply of the branchio- 
mandibularis is derived from a terminal twig of the fused ven- 
tral branches of the first, second and third occipital nerves 
(equivalent to Furbringer’s nerves z, a and b). MeMurrich (83), 
though unable to trace the innervation of this muscle in Amia, 
pointed out that it was the probable forerunner of the muscles 
of the tongue of higher forms, and that, as no trace of the 
branchio-mandibularis is to be found in teleosts, Amia was 
probably the last piscine form to possess it. This muscle was 
found in Acipenser by Vetter (95), in Polypterus by Pollard 
(86) and Edgeworth (1. c.) and in Polyodon by Danforth (16). 
In the latter animal the branchio-mandibularis is a very small 
muscle whose innervation was not actually determined but whose 
relations, when compared with Amia, left no doubt as to its 
complete homology with the similarly named muscle in that 
form. 
In correspondence with the evident reduction of these periph- 
eral elements in ganoids as compared with sharks, a reduction in 
the number of spino-occipital nerves has occurred in the former 
eroup. The most rostral of these nerves found in the ganoids is 
Furbringer’s occipital nerve x which occurs in individual cases 
in Acipenser alone, while the occipital nerve z is the only one of 
this sub-group of nerves which is characteristically retained in 
all ganoids. 
Within the central nervous system, one expression of these 
peripheral changes 1s to be seen in the oblique caudal course which 
the emergent spino-occipital rootlets take from their nucleus to 
the periphery—as if the somatic motor column were pushed 
rostrad, dragging with it the remaining motor rootlets. Acipen- 
ser alone proves an exception to this rule and according to Fur- 
bringer it is just this form among ganoids that shows the least 
reduction in the number of occipital nerves. It is also signifi- 
cant to note in this connection that alone among ganoids, coraco- 
