1016 



Amniotes the first pronephric tubule is found as a rule in the third 

 somite behind the skull (Frokiep, 1905, p. 119). The relation between 

 myotomes and gill-slits in this case is not so evident as in lower 

 Chordates. If, however, we take as an example the instructive figure 

 given by van Bemmelen (1889, p. 254) for the head of Lacerta, I 

 think we may deduce from it as the most probable conception 

 that the anteriormost occipital myotome figured corresponds to the 

 first somite following behind that of the primary vagus, being 

 accordingly the Ihird post-otic (just as in Amphibians and Selachians), 

 and the last epibranchial one. 



This is the first of the five myotomes, which after van Bemmelen 

 give rise to the hypobranchial or tongue-musculature, while Corning 

 (1895, p. 165) denies the participation of this first one, only the 

 four anterior post-branchial myotomes according to his statements con- 

 tributing to it. Of these, three belong to the head, while the fourth 

 corresponds to the atlas. Indeed, the tongue musculature is supplied 

 by a hypoglossus with three occipital roots uniting with the first 

 free ventral root (Fürbkinger, 1897, p. 506) to a plexus cervicalis 

 which, however, in this case does not fuse with the plexus brachialis, 

 which in Amniotes often shoves backwards pretty far from the head. 



Thus the hypobranchial resp. tongue-musculature of Vertebrates in its 

 origin and innervation wholly agrees with that of the paired limbs. 

 To the hypobranchial m u s c u 1 a t u r e a 1 s o t h e r u 1 e 

 formulated by Fürbringer (1879, p. 389) for that of the 

 extremities is applicable, that the structure and inner- 

 vation is not bound to distinctly numbered segments but that the 

 place and number of the latter depends upon the situation and 

 extension of the "segmental level" from which the organ takes its 

 origin. Displacement in forward and backward direction, extension 

 and reduction is possible without the myotomes themselves moving, 

 dividing or fusing, or new myotomes being intercalated or others 

 falling out. The anterior limit of the hypoglossus region is always 

 determined by the situation of the last gill-slit and so by the number 

 of gill-slits. Possibly also the hindmost epibranchial myotome can 

 participate, though among the observations cited above there is only 

 one concerning this point (Miss Platt, 1897) which has not met 

 opposition, nor does the non-participation of the corresponding ventral 

 root exclude every possibility of doubt. 



It also depends on the number of gill-slits whetlier the anterior 

 hypoglossus roots come to lie within the sphere of influence of the 

 vagus, and, together with the primarily epibranchial nerves, may be 

 considered with some right as ventral roots of the partially polymeric 



