Literary Notices. xxv 



nected with the thalamic ganglion by a fibrous strand. From the brain 

 to the thalmic ganglion Hoffmann calls this nerve the "thalamic," from 

 the ganglion distally, the "ophthalmicus profundus." 



The ventral nerve for the second somite is lost, the dorsal nerve 

 being the " trochleo-trigeminus." This nerve gives rise to the troch- 

 learis and all of the trigeminus except the r. ophthalmicus profundus. 

 Its gill slit and gill bar are lost. Its ganglion is termed the g. trigemini, 

 and the term g. Gasseri is applied to the fused product of the union of 

 the g. trigemini and the g. ophthalmici. The abducens is the ventral 

 nerve of the third somite, its dorsal nerve is the " ophthalmico-buc- 

 calis," viz., the r. ophthalmicus superficialis facialis and ther. buccalis. 

 The ophthalmic represents the dorsal branch and the buccal the post- 

 trematic ramus of the ventral branch, primitively running out on the 

 mandible. 



The fourth and fifth somites have no ventral nerves. The dorsal 

 nerve of the fourth is the " acustico-hyoideo-mandibularis," the acus- 

 ticus representing the dorsal branch and the hyoideo-mandibularis the 

 post-trematic ramus of the ventral branch. The palatine and pre- 

 trematic branches run down m the typical way in front of the spiracle, 

 this being the first segment to exhibit all of the typical branches of a 

 branchial nerve. The fifth somite is in the same way related to the 

 glossopharyngeus, this nerve forking around the first true gill cleft in 

 the typical way. 



As a matter of fact the relations in the adult do not accord with 

 this scheme, for the trigeminus does not form the ventral branch of a 

 branchial nerve in front of the mandible, nor does the buccalis form 

 the ventral branch of the segment containing the mandible. The au- 

 thor, not finding any evidence of the suppression of a branchiomere 

 between the mandible and the hyoid, therefore assumes that there has 

 been a degeneration of gill arches and clefts progressing caudad and 

 that the ventral ramus of the trigeminus thus came to He in the man- 

 dible as a secondary arrangement. The proper nerve of the mandible 

 was then crowded out of its own segment and suffered change of func- 

 tion to supply the infra-orbital lateral line canal. 



This argument seems to the reviewer forced and unnatural. But 

 the original and primary metameric scheme upon which the argument 

 is based exhibits a much more fundamental defect; viz., the old error 

 of homologizing disparate structures. The dorsal branches, for instance, 

 of his pre-otic nerves are in some cases general cutaneous and in other 

 cases lateralis nerves. It may be regarded as thoroughly established 

 that the whole lateral line system is cenogenetic and possesses abso- 



