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"Lateral view of Amphioxus. The notochord runs from tip to tip. t., Tentacular cirri; G., reproductive organs; a.p., atriopore; a., position of anus; 40 and 62, indicate number of myotomes." -Thomson, 1916

Lancelet

"Lateral view of Amphioxus. The notochord runs from tip to tip. t., Tentacular cirri; G., reproductive…

Scheme to illustrate the disposition of the myotomes in the embryo in relation to the head, trunk, and limbs. The muscles eventually form from these myotomes. Labels: A,B,C, First three cephalic myotomes. N,1,2,3,4, Last persisting cephalic myotomes. C,T,L,S,Co., The myotomes of the cervical, thoracic, lumbar, sacral and caudal regions. I.,II.,III.,IV.,V.,VI.,VII.,VIII.,IX.,X.,XI.,XII., Refer to the cranial nerves and the structures with which they may be embryologically associated.

Myotomes in an Embryo

Scheme to illustrate the disposition of the myotomes in the embryo in relation to the head, trunk, and…