760 EEPOET OF COMMISSIONER OF FISH AND FISHERIES. [14] 



precisely the same topographical relations to neighboring ossifications 

 of the skull, to the suprascapula, and to the foramen for the exit of 

 the vagus and the glossopharyngeal. 



The nerve situated most anteriorly in the occipital region is the 

 glossopharyngeal. Its foramen of exit is found where the intercalare, 

 the petrosal, and the cartilaginous portion of the primoidal cranium 

 come together, and below and between the basioccipital and petrosal 

 (Plate I, Figs. 2 and 3, gph.). Immediately after its exit from the fora- 

 men the glossopharyngeal divides into its two well-known branches, 

 the distribution of which is of no interest in the present connection. 



Thoroughly separated from the glossopharyngeal foramen we find 

 the foramen for the vagus is so located in the suture between the inter- 

 calare and theoccipitale laterale that its periphery is formed by these two 

 bones (Plate I, Pigs. 2 and 3, vJ^^). The nerve itself exhibits essentially 

 the same behavior after its exit as in the Teleostei. 



While yet within the brain-case the A^agus gives off a very minute 

 branch, which, ascending upwards, perforates the cartilaginous skull- 

 cover beneath the parietal, into which it enters, probably to supply its 

 mucus canal. I should not have mentioned this little branch at all if 

 the so-called ramus lateralis nervi trigemini, which is known to receive 

 fibers from the trigeminus and from the vagus, did not quit the cranium 

 at the same locality in many of the Teleostei. That this nerve in Arnia 

 also receives fibers through its anastomosis with cranial nerves that 

 arise more anteriorly I have once been able to confirm, but, in conse- 

 quence of the indifferent manner in which the specimen I examined had 

 been preserved, it was impossible to ascertain from which nerve this 

 anastomosis proceeded. While the occipital region of the Selachians" 

 arrives at its posterior limits with the vagus, in fishes provided with 

 ossified skulls several nerves of the occipital group, and of a character 

 identical with the spinal nerves, are constantly to be found between the 

 vagus and the first spinal nerve. 



Amia, possessing the largest number hitherto observed of occipital 

 nerves, furnishes us with three such for our consideration. The most 

 anterior of these leaves the brain-case at a minute foramen in the occip- 

 itale laterale, and situated near its posterior border (Plate II, Fig. 4, oc 

 I). It is of a smaller caliber than the two following, and also differs from 

 them in that it only arises from the spinal cord by means of an anterior 

 root. The nerve next in order arises by both an anterior and posterior 

 root, between the hinder border of the occipitale laterale and the ante- 

 rior occipital arch (Plate II, Fig. 5, oc II). Immediately after their 

 exit these two roots unite in a common trunk, and in so doing carry out 

 the character of a spinal nerve (Plate II, Fig. 5, oc III). The first 

 spinal nerve in Amia quits the neural canal between the posterior occi- 



26 Marked vg. in original text. — Trans. 



2' As a matter of course only such Selachians are here taken into consideration whose 

 crania are sharply defined from the vertebral column. 



I 



