332 



version into locomotor and fixing organ), it follows that the nervous 

 elements of the praeoral lobe (apical plate and cerebral ganglion) 

 must be entirely lacking in the Vertebrates, while its mesodermal 

 element is represented by the praemandibular head-cavities which give 

 rise to most of the eye-muscles. 



In consequence of the great development and forward growth of 

 the brain even in the lowest craniate Vertebrates as compared with 

 Amphioxus and the Ascidian larva, and in consequence too of the 

 cranial flexure, the praeoral (praemandibular) head-cavities have been 

 made to assume more subservient topographical relations and no longer 

 assist in the formation of a prominent lobe in front of the body. 



New York, February 15., 1894. 



Nachdruck verboten. 



The Arrangement of Mnscnlar Fibres in Amphiuma tridactyla. 



By Alvin Davison, M. A. Fellow in Biology, Princeton College, U. S. A. 



With one Figure. 



Through the kindness of Mr. McClure who has placed at my 

 disposal a large number of Amphibians and otherwise aided me with 

 numerous suggestions, I have been able to make the following investi- 

 gations in the arrangement of the muscular fibres of Amphiuma. 

 A copious supply of literature on the muscles of almost all the genera 

 of Amphibians except this one, is at hand. I am not aware that 

 any one has offered an explanation or even given a 

 description of the peculiar arrangement of the muscu- 

 lar fibres of Amphiuma. 



As my investigations on this subject are not yet completed, I 

 will present in this article only a brief description of the fibre arrange- 

 ment displayed in the muscles of the tail and back. The fascial 

 investment consists of a dense sheath of tissue arising from the neural 

 spines in two plates which scarcely separated at their origin, diverge 

 gradually as they rise to the dorsal surface thereby bounding laterally 

 a triangular area filled with connective tissue and a fatty substance 

 along the mid-dorsal line. Each plate is reflected over the external 

 surface of its respective side, and so closely and firmly does it adhere 

 to the coriaceous skin that a sharp knife is required to effect the 

 separation. At a distance of one-fifth the circumference from the 

 dorsal line, the fascial envelope divides, sending the lamina split off, 



