THE MUSCULAR SYSTEM 



285 



ogists to assume that their development corresponds in essentials through- 

 out the vertebrate series. 



lEUfWL PLATt 

 NOTOCMORO 



URAL fl>TE 

 McSOOCRM 



rCURAL 

 SOMATIC 



ECTOOERI 



NCTTOCHOflO 

 NOTOCHORO 



COELOM 

 ENDODERM 



EHX}0£RM 

 ENTERON 



SPU^NCMN 

 ECTODERM MESODERM 



EhfTEHOI 



SOMATIC MOTOR 

 NERVE 

 iTIC MOTOR tCR>t 

 MYOTOME 

 EPIMERE MYCTTOME 



DERMATOME 

 NCSOhCRE 



NOTOCHORD 

 COELOM 

 HYPOMERE 

 MESENCWME ^O^TA' 



IDERM ENTE 



ITERON keSEN 



ICTOOERM ENtXDOi 



(SPINAL CORD 



SPINAL 

 DORSAL ROOT GANCJJONi 



EPAXIAL MUSCLI 

 "^ NOTOCHORI 



GONAD 



NTESDNE 



RITONEUM 



SCERAL MUSCLE 



HEMAL ARCH 

 DORSAL AORTA- 

 LATERAL ur 

 CARDINAL VE 

 PRIMITIVE DUCT- 

 MESOrCPWIC TUBULE 

 HYPAXIAL MUSCLE- 

 CONA 



Fig. 236. 



-A series of diagrams A-F illustrating the ontogenesis of muscles in vertebrates. 

 (Based upon figures by Hatschek and Kingsley modified.) 



Their development has been most thoroughly investigated in elasmo- 

 branchs. In embryos of this group, as well as in higher vertebrates to 



hyp.n 



Fig. 237. — Diagram of muscle segments in head of embryo vertebrate, based upon a 

 shark. The anterior myotomes tend to divide into dorsal and ventral moieties; 

 persistent myotomes lined, transient with broken lines; central nervous system dotted, 

 nerves black, a, premandibular somite; abd, abducens nerve, hyp, hypoglossal muscula- 

 ture; hypn, hypoglossal nerves; om, oculomotor nerve; sp, spiracle; 1-6, first six somites 

 (4, 5, 6, functional in Petromyzon) ; I-VIII neuromeres. (From Kingsley's "Com- 

 parative Anatomy of Vertebrates," after Neal.) 



mammals, the eye muscles develop from somites or "head cavities." 

 The first head cavity (somite i) gives rise to the four muscles innervated 

 by the oculomotor nerve, the superior oblique muscle comes from the 



