230 F. U. EDGKWORTII. 



increase in size of tlie jaws, there is a gradual overlapping of 

 tlie hyoid bar by the mandibular skeletal structures, with 

 associated secondary changes in the muscles. Thus, the 

 levator hyoides shifts its insertion from tlie hyoid bar to the 

 hind end of Meckel's cartilage in Amphibia and Sauropsida, 

 and the intermandibularis partially underlies the iuterhyoi- 

 deus in Selachii, Teleostomi, Ceratodus, and Urodela. It is 

 probably in connection with this overlapping that the hyo- 

 maxillaris Aniage becomes a ligament in Urodela, Cera- 

 todus, and some Teleostomi, and is not developed in 

 Selachii and Sauropsida. 



Eye Muscles of the Rabbit. 



The development of the external ocular muscles in Teleo- 

 stoman and Amphibian embryos was not followed. 



In pig embryos of 10 mm. maximum and 6 mm. Nacken- 

 lange, Reuter found the Aniage of the eye muscles as an 

 " untrenubarer Zellcomplex,^' which, he held, " als Anhau- 

 fung von morphologisch urspriinglich Keimzellen aus dem 

 Mesenchym hervorgeht." 



In 3 mm. embryos of the rabbit the premandibular Aniage 

 is developed, on each side, as a hollow outgrowth of the fore 

 end of the alimentary canal (Text-fig. 75). This outgrowth 

 becomes solid by proliferation of its walls as it is constricted 

 off, and in 3| mm. embryos (Text-fig. 79) it forms a solid mass 

 connected with its fellow by a solid string of cells lying across 

 the fore end of the alimentary canal just below the anterior 

 down-turned end of the notochord. The connecting string 

 of cells has disappeared in 4^ mm. embryos. The premandi- 

 bular Aniage forms a crescent-shaped mass in 4 mm. embryos 

 (Text-fig. 84) ; and from this the recti superior, inferior, 

 internus, and obliquus inferior are formed (Text-figs. 96, 97). 

 The obliquus superior is formed from the anterior extremity 

 of the upper end of the mandibuhir myotome in 3^ mm. 

 embryos (Text-fig. 78). The development of the abducens 

 Aniage is doubtful ; in 3^ mm. embryos it is visible lying 



