SECTION THROUGH PHAHYNX. 



201 



B. Transverse Section through the Anterior Part of the 

 Pharynx. 



1. General characters. The section is triangular in shape, 

 the apex being formed by the dorsal fin, the base by 

 the ventral surface, and the basal angles by the 

 metapleural folds. The pharynx, perforated by the 

 gill-slits, aqd surrounded by the atrial cavity, lies 

 below the notochord. 



Fig. 41. — Amphiozas lanceolatus. — Transverse section through the 

 anterior part of the pharynx of an adult specimen. The boundary 

 of the atrial cavity is indicated by a thick black line. (a. m. m.) 



A, skeleton of dorsal fin. B, spinal cord. C, notochord. I>, counectlTe- 

 tissue sheath surrounding notochord. E, cavity of pharynx. P, epibranchial 

 groove of pharynx. G, endostyle, which in this anterior part is flattened out or 

 even convex. H, atrial, cavity. J, transverse muscles in floor of atrial cavity, 

 M, dorsal ccBlomic canal. P, metapleural canal. H, left dorsal aorta. S, 

 endostylar ccnlomic canal in which tlie cardiac aorta lies. X, myotome. Y, 

 suspensory fold of pharynx, separating the dorsal coelomic canal from the atrial 

 cavity. Z, gill-arch or branchial bar ; the triangular white spot lepresents the 

 cut surface of the skeletal rod of the arch. 



