308 F. H. EDGEWORTH. 



secondary innervation from cervical segments — first, second, 

 and third in man, first and second in the dog — but it is 

 not known whether this is due to backward migration or to 

 local development of motor neuroblasts. 



On the Size of the Medullated Nerve-Fibres Passing to 

 Cranial Muscles. 



Claskell stated that in the dog large fibres, 14"4 to 18 ju in 

 diameter, were present in the Ilird (external ocular muscles), 

 IVth, Vltl), Vllth (destination not traced), and Xllth. 

 The corresponding muscles were considered to be somatic. 

 Nerve-fibi*es not exceeding 10"8 fi in diameter were found in 

 Yllth (facial muscles), pharyngeal nerves, and recurrent 

 laryngeal ; and the corresponding muscles wei-e considered 

 to be splanchnic. Apparently he did not take the size of the 

 nerve-fibres as the sole criterion of the somatic or splanchnic 

 nature of a muscle, for the stern o-mastoid and trapezius 

 were considered to be splanchnic, though the nerve (spinal 

 XTth), showed the larger size of nerve-fibres. A further 

 analysis (loc. cit.) of the size of nerve-fibres passing to cranial 

 muscles in the dog shows that : (1) In any individual nerve, 

 fibres are found of all sizes up to the largest present ; (2) the 

 nerve-fibres taper very slightly as they pass from the central 

 nervous system to the muscles; (3) if comparison be made 

 between the maximum size of the nerve-fibres and the 

 morphological nature of the muscles to which they pass, the 

 following results appear : (a) Nerve-fibres of the greatest 

 size (17*6 fx in diameter,^ in some dogs only 16 fj), are found 

 in the nerves of the external ocular muscles, temporal, 

 pterygoids, tensor tympani, digastric (both from Vth and 

 \'IIth), stylo -hyoid, branchio-hyoid, trapezius, sterno- 

 mastoid, genio- hyoid, sterno- hyoid, sterno- thyroid, thyro- 

 hyoid, and omohyoid — all of which, according to the theory 



' This is also the luaxinuim size of the nerve-fibres in the anterior 

 roots of the non-limb portions of the spinal cord. In the limb areas it 

 is slightly greater. 



