262 MR GOODSIR ON THE ANATOMY OF AMPHIOXUS LANCEOLATUS. 



EXPLANATION OF PLATES IV. V. 



PLATE IV. 



Fig. 1. A lateral view of Amphioxus lanceolatus. As the specimen when sketched was slightly com- 

 pressed between two plates of glass, it is represented of greater depth than the animal exhibits in its 

 natural condition, a The mouth, with the oral filaments ; b the abdominal fold of the left side ; the 

 fold is semitransparent, so that the lower surface of the abdomen is seen through it ; c the anus, with 

 one fin before, and another behind it ; d the dorsal fin ; the vesicular germs of the rays are seen in 

 all these fins, and the splanchno-ribs are also visible through the abdominal parietes ; e the length 

 of the specimen. 



Fig. 2. The abdominal aspect of the specimen, a The mouth ; b 6 the abdominal folds ; c the anus ; 

 d the heart. 



Fig. 3. A lateral view of the same specimen after the removal of the integuments, including the abdomi- 

 nal folds, and the soft parts of the fins, a The mouth, with the oral filaments ; b the abdominal 

 muscle, with the splanchno-ribs seen through it ; c c the heart ; d the anus ; e the vesicular germs 

 of the rays of the anterior ; / those of the posterior anal fin ; these germs do not, like the soft parts, 

 extend to the extremity of the tail ; g the germs of the rays of the dorsal fin, which, like those of the 

 anal fin, do not extend along the tail ; h h the lateral muscular bundles separated by the needle, so 

 as to display in their intervals the " chorda dorsalis," and the dorsal and ventral branches of the 

 nerves ; i the first pair of nerves ; k the second pair, analogous to the trifacial, the dorsal and ventral 

 branches of which extend along the bases of the fins to join the branches of the other nerves. This 

 dissected specimen is flattened by slight compression, in order to display the various parts with 

 greater distinctness. 



Fig. 4. The integuments have been removed from the tail, but the abdominal folds have been left. The 

 . abdominal muscle, and the branchial compartment of the intestinal tube, have been opened longitu- 

 dinally, a little to the right side of the mesial line, a a The two divisions of the hyoid bone ; b b the 

 internal surface of the branchial chamber, through the walls of which the " chorda dorsalis," the 

 nerves, and the ventral bundles of the muscles, are seen ; c c the heart, with the splanchno-ribs 

 passing off from it on each side towards the " chorda dorsalis ;" d d the abdominal muscle ; e the 

 digestive portion of the intestinal tube proceeding to the anus ; f gg the abdominal folds. 



Fig. 5. The neuro-skeleton, consisting of a a the " chorda dorsalis," 6 6 the vesicular germs of the dorsal 

 fin rays, c those of the anterior, and d those of the posterior anal fins. 



Fig. 6. The nervous system, a a The spinal cord ; b the first pair of nerves ; c the dorsal; d the ventral 

 branch of the second pair. 



Fig. 7- The intestinal system, a The branchial compartment ; 6 the digestive compartment of the intes- 

 tinal tube ; c the mouth ; d the anus. 



Fig. 8. The vascular system, a a The heart ; 6 b the primary branches, or branchial arteries ; c c the 

 branchial veins uniting in loops, from the angles between which, trunks convey the blood into a a the 

 aorta. 



