MOKPHOLOGY OF CKAXIAL MUSCLES IN SOME VERTEBRATES. 237 



levator iu Sh mm. embryos (Text-fig. 22), and grows back to 

 the shoulder-girdle; in 11 mm. embryos its fore part has dis- 

 appeared, and the anterior end of the part remaining is 

 attached to the skin ; in the adult it is absent (Vetter). The 

 portion of the fifth branchial myotome above the coraco-bran- 

 chialis Y forms a muscle attached above the fourth epi- 

 branchial and below to the fifth cerato-branchial — the fifth 

 levator of Vetter. 



In Amia the lower end of the fifth branchial myotome forms 

 in 8i mm. embryos (Text-figs. 31, 32) the lateral half of a 

 transversus ventralis V and a coraco-branchialis V, as in 

 Acipeuser ; tlie lower end of the fourth branchial myotome 

 forms ( rex:-fig. 30) the lateral half of a transversus ventralis 

 IV and the Aulage of the interarcualis ventralis IV, which 

 PTOws forwai-d to the third branchial bar. Neither coraco-bran- 

 chiales^ nor interarcuales ventrales are formed in the first 

 three myotomes ; the lower ends of the myotomes grow 

 downwards and inwards, forming tlie ventral portions of the 

 obliqui ventrales 1, 11, and 111. The portion of the fourth 

 myotome, next above the Aidagen of the interarcualis ven- 

 tralis IV and transversus ventralis IV, forms the obliquus 

 ventralis of that arch, which is serially homologous with the 

 dorsal portions of the obliqui veuti-ales of the first tlu-ee 

 arches. In 15 mm. embryos the hind end of the interarcualis 

 ventralis IV grows backward to the fifth bar, and in 

 19 mm. embryos its front portion divides longitudinally into 

 two (Allis), so that there are formed two longitudinal muscles 

 extending from the third bar to the fourth and fifth respec- 

 tively ; both are innervated by the nerve to the fourth arch 

 (Allis). 



Allis homologised these longitudinal muscles with the 

 lower portions of the obliqui ventrales of the first three 

 arches, but their development shows that the latter are homo- 



' Filrbrhiger described a curaco-ljrancliialis II. lint it is not des- 

 cribed by Allis or McMurricli, and was not present in the eniljryos 

 examined. 



