SECTION THEOUGH PHAEYNX 



185 



B. Transverse Section through, the Anterior Fart of the 

 Pharynx. 



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

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

 the ventral surface, and the basal angles by the lateral 

 fins. The pharynx, perforated by the gill-sUts, and 

 surrounded by the atrial cavityj lies below the noto- 

 chord. 



Fig. 32. — Amphiozss lanceolatns. 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. D. connective- 

 tissue sheath surrounding notochord. E, cavity of pharynx. I", hyper- 

 branchial groove of pharynz. G. hypobranchial groove of pharynx, which in 

 this aniierior part is flattened out or even convex. H, atrial cavity. J^ trans- 

 verse muscles in floor of atrial cavity. M, dorsal coelomic canal, P, meta- 

 pleural coelomio canals. H, left dorsal aorta. S. cardiac aorta. 3^. myotome. 

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

 atrial cavity. Z, gill-arch or branchial bar. 



