SECTION THKOUGH PHAEYNX 



185 



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 lateral 

 fins. The pharynx, perforated by the 'gill-slits, and 

 surrounded by the atrial cavity, lies below the noto- 

 chord. 



FIG. 32. Amphioxus 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. D, connective- 

 tissue sheath surrounding notoohord. E,, cavity qf pjiarynx.- P, .hyper- 

 branchial groove of pharynx. G, nypobranchial groove of pharynx, which in, 

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

 verse muscles in floor of atrial cavity. M, dorsal co?Iomic canal. P, meta- 

 pleural coelomic canals. B,, left dorsal aorta. S? cardiac aorta. X, myotome. 

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

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



