CLASSiriCATION OP THE ANIMAL KIKGDOM. 21^ 



described by Elathke, whicb answer to tbe velum of Amphioxus. 

 But the dorsal ends of the attached edges of these folds are 

 situated immediately under the middle of each auditory capsule ; 

 and, in the adult Lamprey, they can be proved to correspond 

 with the position of the hyoidean arch. In the Amphioxus their 

 dorsal attachment corresponds with the anterior angulation of 

 the intermuscular septum between the sixth and seventh myo- 

 tomes, counting from the anterior end of the body. Hence, it 

 follows that this septum answers to the hyoidean arch of the 

 higher Vertebrata, and that the six myotomes in front of it re- 

 present six primary segments of the body, or somatomes. But 

 the first of these lies behind the eye, whence it also follows that 

 the region occupied by these somatomes answers to the region in- 

 cluded between the optic foramen and that for the seventh nerve 

 in the skull of an ordinary vertebrated animal, and that so much 

 of tlie head of Amphioxus as lies in front of the hyoid region 

 answers to the prgeauditory moiety of the skull in other Ver- 

 tebrata. 



In Amphioxus, a nerve leaves the cerebrospinal axis in cor- 

 respondence with the interval between each pair of myotomes, 

 and then divides into a dorsal and a ventral branch, like an ordir 

 nary spinal nerve. And, in front of the first myotome, two nerves, 

 or perhaps one nerve in two divisions, are given ofi". The more 

 anterior of these two passes above the eye, and is distributed to 

 the end of the body in front of the mouth, while the second and 

 the other nerves pass to the side walls of the oral cavity. 



These nerves, arising as they do between the homologue of the 

 optic nerve and that of the portio dura, must represent the third, 

 fourth, fifth, and sixth pairs of cranial nerves of the ordinary Yer- 

 tebrata ; while the myotomes between which five of them pass 

 must represent the muscles of the nose, eye, and jaws. In fact, the 

 course of the most anterior nerve is exactly that of the orbito- 

 nasal nerve (the so-called ophthalmic, or first, division of the tri- 

 geminal), as is conspicuous when this nerve in Amphioxus is com- 

 pared with the undoubted orbito-nasal of the Lamprey. 

 - In the embryo Lamprey, at the most advanced stage described 

 by Schulze, the portion of the centro-spinal axis which lies between 

 the ear and the eye is relatively very long ; but the cerebral hemi- 

 spheres are beginning to grow out beyond the primitive anterior 

 end of the cerebro-spinal axis, and project beyond the eye. In the 

 :.young Ammocoetes of 1*5 inch long the length is still great, though 



