MORPHOLOGY OF CRAXIAL ^[[JSCLES IX SOME VERTEBRATES. 267 



first, second, and third' interbasales of Scy Ilium are developed 

 in 23 mm. embryos from the first, second, third, and fourth 

 spinal myotomes (Text-figs. 12, 13, 14), by growths from their 

 ventral edges internal to the ganglia of the ninth and tenth 

 nerves. 



A retractor arcuum branchialium dorsalis is found in 

 some Teleosteii (Vetter), e. g. Perca and Cyprinus, in Amia 

 (Allis, AViedersheira-), and in Lepidosteus (Wiedersheim"), 

 but is not present in Polypterus (Pollard), or in Salmo f ario. 

 In Amia the muscle, which is inserted into the third infra- 

 pharyngo-branchial, arises according to Allis from the third 

 and fourth, according to AViedersheim fiom the seventh and 

 eighth, vertebral bodies. In Lepidosteus the muscle is 

 inserted into the third infrapharyngo-branchial, and arises 

 from the lateral surface of the third and fourth vertebral 

 bodies (Wiedersheim). The retractor was supposed by Allis 

 and by Wiedersheim to belong to the system of the levatores 

 arcuum branchialium. 



The muscle is developed in Amia from downgrowths from 

 the lower surface and lower part of the internal surface of the 

 sixth to thirteenth trunk-myotomes in 8h mm. embryos (Text- 

 fig. 33); these downgrowths form a longitudinal muscle, the 

 anterior end of which grows forward to the third bar. Its 

 development in Lepidosteus is similar, taking place, in 12 mm. 

 embryos, from the third to ninth trunk-myotomes. 



Hypobranchial Spixal Muscles.'^ 



In Scyilium, van Wijhe stated that the coraco-hyoideus 

 was developed from venti-al prolongations " sowohl des hin- 

 sterstenKopfmj'otomes als die der vorderenRumpf myotome," 

 and that the coraco- branchiales and coraco-mandibularis 

 were formed from the walls of the " unpaaren vorderen 



' The tlurd iuterhasalis. devek)ped in the embryo, is not described iu 

 tlie adult by Filrbringer. 



- Retractor laryngis of Wiederslieiiu. 



^ This name is used in the sense stated aljove. 



