MR GOODSIR ON THE ANATOMY OF AMPHIOXUS LANCEOLATUS. 263 



PLATE V. 



Fig. 1. a Portion of the " chorda dorsalis," to show the circular fibres of the sheath ; I the superior ; 

 c the inferior longitudinal ligament. 



Fig. 2. A portion of the sheath ; shreds of the aponouroses adhere to it. 



Fig. 3. One of the compressed vesicles which occupy the interior of the sheath, and compose the mass of 

 the " chorda dorsalis." 



Fig. 4. Some of the compressed vesicles removed from the sheath, to shew their relation one to another. 



Fig. 5. Five of the cylindrical cells, from the dorsal fin, to shew their relative positions, and the masses 

 of cells which they contain in their interior. 



Fig. 6. A single cell. 



Fig. 7- A portion of the spinal cord, from its anterior third, magnified, to shew the black matter which 

 runs along the median line, and the origins of the nerves. 



Fig. 8. A portion of the middle third, highly magnified to shew the nucleated cells of which it is com- 

 posed, and the larger cells of the dark median band. Some of the cells of the dark band are filled 

 with black pigment granules, which are represented escaping under the compression. 



Fig. 9. A portion of the spinal cord, magnified to shew the origin of the nerves by single roots, and with- 

 out the insertion of the primitive fibres of the nerves into the substance of the cord. 



Fig. 10. Primitive fibres of a nerve. 



Fig. 11. A transverse section of the spinal cord, to shew the groove on its upper surface, and the black 

 matter on the floor of the groove. 



Fig. 12. Primitive fibres from one of the lateral muscles. 



Fig. 13. The eighteen pieces of one of the divisions of the hyoid bone. The anterior piece carries no ray. 



Fig. 14. A few of the splanchno-ribs to shew their relations to the heart, aorta, and branchial vessels, 

 a a The ribs which bifurcate ; b b the simple ribs ; c c a portion of the heart with four branchial 

 arteries ; d d a portion of the aorta with eight branchial veins. 



Fig. 15. A portion of the aorta to show the mode of connection between the aorta and branchial venous 

 trunks and loops. 



Fig. 16. A portion of the heart to shew the mode in which the arteries leave it. The heart or ventral 

 vessel is somewhat flattened, its upper and under walls meeting at an acute angle on each side. 



Fig. 17. The lower end of one of the lateral muscular bundles, magnified to shew th6 position and con- 

 figuration of one of the generative organs. 



Fig. 18. Portions of four pieces from the hyoid bone, magnified to shew the mode of connection, also 

 the cavities, and irregular masses of cells which they contain. 



Fig. 19. One of the generative organs, highly magnified under compression, to shew the nucleated cells 

 of which it is composed. 



VOL. XV. PART I. 4 B 



