1874. j 113 [Gray. 



So, in describing the structure of the optic nerves in the 

 frog, and the development of the eye and optic lobes, he pro- 

 ceeds to remark, that — 



" The instances of Proteus and Amblyopsis naturally sug- 

 gest the questions, whether one and the same part may not 

 combine functions wholly different in different animals, and 

 whether the same may not hold true with regard to the cere- 

 bral organs which is known to obtain with regard to the 

 skeleton, the teeth, the tongue, and the nose, that identical 

 or homologous parts in different animals may perform func- 

 tions wholly distinct. If the doctrine here suggested can be 

 admitted (and if this were the place facts could be cited in 

 support of it), may we not find in it an explanation of many 

 inconsistences which now exist between the results of com- 

 parative anatomy and of physiology ? " 



Then, in his chapter on the philosophical anatomy of the 

 cranial nerves and skull, after showing that there are but 

 three pairs of cranio -spinal nerves, he takes up the contro- 

 verted question as to the number of vertebraa which compose 

 the skull, and supports the opinion that they also are only 

 three in a characteristic manner. 1 



Of this whole memoir it is thought that, notwithstanding 

 the great advance which has been made in comparative anat- 

 omy during the twenty-five years which have elapsed since 



1( 'The conclusions which have been drawn from the statements made above 

 are as follows : that in frogs the vagus comprises the glosso-pharyngeal and acces- 

 sory nerves ; that the trigeminus comprises the facial, the abducens, and in the 

 salamanders the patheticus and portions of the motor communis; that other evi- 

 dence sustains the hypothesis, that the whole of the motor communis is a depend- 

 ence of the trigeminus; if to these we add the hypoglossus (which in frogs is 

 exceptionally a spinal nerve), we shall have three pairs of cranial nerves, each 

 having all the characters of a common spinal nerve, namely, motor and sensitive 



PROCEEDINGS B. S. N. H. — VOL. XVII. 8 NOVEMBER, 1874. 



