268 r, n, ei)(;kwoj(TH. 



Verliiugerang des Pericardia ms." Xeal, in Squalus acan- 

 thias, found that the Anlag-e of the hypoglossus musculature 

 was formed from the fourth to the eighth post-otic myotomes 

 by buds which separate and come to lie ventral to the 

 branchial basket; they do not fuse into a common cell mass, 

 but show their primary metamerism, the bud from the fourth 

 myotome coming to lie between the hyoid and mandibular 

 cartilages and forming "in part the Anlage of the proper 

 tongue muscles," whilst "the four following myotomic buds 

 come to lie between the hyoid and procoracoid." 



I find that inScyllium the initial stages of the development 

 of the coraco-mandibularis and coraco-hyoideus are similar to 

 those of Squalus acanthias,as stated by Neal. This stage 

 is completed in 16 mm. embiyos, and is immediately followed 

 by one (17 mm.), in Avhich the hind end of the primitive 

 genio-hyoideus, which does not becoine affixed to the hyoid 

 bar, grows backwards along the median edge of the coraco- 

 hyoideus towards the shoulder-girdle — forming the coraco- 

 mandibularis (Test-figs. 11, 12, lo). 



The coraco-hyoideus of Salmo salar (Harrison) is 

 developed from ventral downgrowths of the second, third, 

 and fourth trunk myotomes, which bend round the pharyngenl 

 region, and form a longitudinal column, the anterior edge of 

 which extends forwards to the hyoid bar. A similar develop- 

 ment of the hypobranchial spinal muscles takes place in 

 Acipenser, Lepidosteus, Amia, and Salmo, occurring in 8 mm., 

 8 mm., 7 mm., and 5 mm. embryos respectively, and in each 

 case from the second, third, and fourth trunk myotomes. In 

 Salmo fario and in Lepidosteus the forward growth of the 

 anterior end reaches the hyoid bar only, so that only a coraco- 

 hyoid is formed. In Acipenser and Amia it extends further, 

 to the symphysis, reaching this in Sh mm. embryos of 

 Acipenser (Text-figs. 21, 22), and in 8 mm. embryos in Amia. 

 The long column then divides at the level of the hyoid 

 bar into an anterior and a posterior group — the genio-hyoid^ 



' Brancliio-iiKiiKlihaliiris of Vetter and A His. 



