280 F. H. EDGEWOETH. 



evidence available. The cranial muscles form one item only 

 of such evidence, but it is of interest to inquire how far their 

 morphology falls in with generally received opinion, and in 

 what direction it points in cases where opinions vary. 



Such an inquiry is beset by the difficulties which arise 

 from — (a) secondary innervation of muscles ; (b) develop- 

 ment of similar changes in various groups ; (c) atrophy, and 

 non-development of muscles. 



(a) Comparison of the development and innervation of the 

 cranial muscles shows that although, iu general, a muscle is 

 innervated by the nerve corresponding to its segment of 

 origin, yet this is not invariably the case. Thns : 



(1) The posterior part of the intermandibularis of Triton 

 is innervated by the Vllth (Driiner).^ 



(2) The intermandibularis of Selachians is, in part, e.g. 

 Scyllium (Vetter), or wholly, e.g. Acanthias (Vetter), inner- 

 vated by tlie Vllth. 



(3) The intermandibularis anterior and posterior (the latter 

 called " inferior genio-hyoid" by Allis) of Amia are innervated 

 by both the Vth and Vllth (Allis). 



(4) The hyo-maxillaris of Teleostomi, developed in the 

 hyoid segment, isinsome, e.g. Menidia (Herrick), wholly in- 

 nervated by the Vllth; whereas in others, e.g. Esox (A-^etter), 

 Salmo, its hinder part is innervated by the Vllth and its fore 

 part by the Vth ; and in Amia (Allis) it is innervated by the 

 Vth and Vllth. 



(5) The anterior digastric of man, pig (Futamura), and 

 rabbit, developed in the hyoid segment, is innervated by the 

 Vth. 



(6) The cerato-hyoideus externus of Urodela, developed in 

 the hyoid segment, is innervated either by the Vllth, e.g. 

 Necturus (Miss Piatt), or by the IXth, e.g. Triton (Driiner). 



(7) The interarcuales ventrales of Urodela are innervated 

 both by the nerves corresponding to their segments of origin 

 and also by those of the next anterior segments (Driiner). 



(8) In some Teleostomi, e.g. Polypterus senegalus, 



' Roman numerals denote cranial nerves. 



