[15] THE OSTEOLOGY OF AMIA CALVA. 761 



pital arch and the ueiirai arch of the first vertebra, prest-'iiting us with 

 uothing of particular note. 



The three occipital nerves, together formiDg- a group, run downwards 

 in front of the shoulder-girdle, to finally ramify, and — probably together 

 with the branch of the first spinal nerve, agreeing in this respect with 

 the corresponding nerves in the Teleostei — to supply the muscles lying 

 between the shoulder-girdle and the mandible. This I could not estab- 

 lish with certainty, for the reason that the specimen used by me for the 

 examination of the nerves had already served for a dissection of the 

 heart and great vessels. To complete the subject, a canal must yet be 

 mentioned, the function of which I have been absolutely unable to dis- 

 cover. It commences on the lateral aspect of the bassioccipital, and 

 on that portion of this bone which so much resembles a vertebra ; it 

 takes a course towards the median plane, turns at a right angle, and 

 terminates at the inferior surface of the bone, between the posterior 

 wings of the parasphenoid. This terminal opening is in close juxta- 

 position with the same opening of the canal of the opposite side, but no 

 communication exists between them nor with the cavum cranii. The 

 contents of this canal I found to be fibrous connective tissue and thin- 

 walled vessels of some caliber (Plate I, Figs. 2 and 3, cb.). 



The fact that free and independent neural arches are found upon the basi- 

 occipital, from between which emerge nerves of a structure like true spinal 

 nerves, is of fundamental importance in the determination of sJculls of the 

 higher fishes, and admits of no other explanation than that lohich applies 

 to the primoidal cranium, the best example of ichich we find in the Se- 

 lachians, tchere we observe anchylosed together a still greater number of 

 vertebrae, with the nerves that pertain to them maMng their proper exits, 



A question still more difficult of determination is to define the num- 

 ber of vertebrae that enter into the comjjosition of the cranium. In Amia, 

 which for this purpose — of all the fishes with osseous skulls examined 

 by me — possesses the best example of this primitive condition, I believe I 

 aui enabled to recognize the elements of three vertebr£e. That the two 

 occipital arches, with the nerves that pertain to them, represent the re- 

 mains of what were originally distinct vertebrae, no reasonable doubt 

 can exist ; and the only question is whether we are to consider the first 

 occipital nerve, which is very feebly developed and without a posterior 

 [dorsal] root, as a rudimentary spinal nerve, or whether another inter- 

 pretation is admissible. 



If the first occipital nerve is not to be considered as a rudimentary 

 spinal nerve, one can see in it — since it is absolutely inconceivable to 

 have a generation of new nerves in the higher animals — but a branch of 

 one of the two neighboring nerves, namely, of the vagus or of the sec- 

 ond occipital nerve, that has branched and become independent. ISTow, 

 the distribution of the first occipital nerve is such, that one cannot for 

 an instant take it to be a branch of the vagus at all, and therefore the 

 only possibility remains that it could belong to the second occipital 



