274 



F. H. EDOEWOin'H. 



Again, there are two inscriptions in tlie coraco-hyoid of 

 Amia (AUis), and Acipenser (Vetter), none in the genio- 

 hyoid. 



The non-development of a genio-hyoid, even as an atrophy- 

 ino- Anhige, in Lepidostens and Salmo wonld appear, on 

 comparison with other forms, to be a secondary condition. 



The developmental history of the hypobranchial spinal 

 muscles suggests that their Anlage was primitively an 

 undivided column, extending forward to the symphysis of 



Text-fig. 77. 



\ tnv^ 



t<^a>A 



77. 



the jaws, an anterior prolongation of the rectus system of the 

 trunk into the head segments. This divided into genio- 

 hyoid and coraco-hyoid. In fishes the genio-hyoid secon- 

 darily extended backwards, overlapping the coraco-hyoid in 

 varying degrees. 



The Anlage of the hypobi'anchial spinal muscles is formed 

 from downgrowths of several — two or more — trunk 

 myotomes, that from the foremost myotome taking part in 

 its formation extending furthest forward, that from the next 

 succeeding it, and so on. There is a certain correlation 

 between the number of trunk myotonies taking part in the 



