82 ON THE MORPHOLOGICAL RELATIONS 



But, in the course of development, the mouth of the ver- 

 tebrate opens through the surface applied against the viteUary 

 mass, whilst that of the annulose animal passes through the 

 aspect turned away from it. The vertebrate mouth is ha3mal, 

 the annulose mouth neural. 



Rathke formerly described the pituitary body as origi- 

 nating in a diverticulum passing up from the pharyngeal 

 mucous membrane through the basis of the embryo skull. 

 I at one time conceived it to be probable that the pituitary 

 body, and the mucous tube, in which, according to Eathke, 

 it originates, might be indications in the vertebrate of a 

 structure which, in the annulose animal, is converted into 

 the mouth. This presumed neural alimentary passage may 

 be conceived as passing up between the bodies of the anterior 

 and posterior sphenoid bones into the Sella Turcica, along the 

 course of the infundibulum to the third ventricle of the brain, 

 and through the cavity of that organ to its upper surface 

 behind the cerebellum, thus leaving the origins of the nerves 

 of smell and vision in the pre-stomal portion of the organ, 

 while the origin of the nerve of hearing would remain in the 

 medulla oblongata or post-stomal portion of the cephalic 

 nervous mass. The arterial circle of Willis, and other pecu- 

 liar arrangements at the base of the skull and brain, appeared 

 to support the view taken. I shall not, however, pursue this 

 hypothesis further, because, from the observations of Eeichert, 

 we know that the base of the cranium is not perforated in the 

 embryo, and that the supposed canal or diverticulum was an 

 incorrect interpretation of the peculiar appearances pro- 



mordial cardiac-arterial tube in all the forms of the embryo vertebrate, and, 

 consequently, with the heart and trunk of the branchial artery of the fish. If 

 this, then, is the real homology of the " aortic trunk " of the crustacean, and 

 if its "brain" is in fact only a pre-stomal portion of its nervous axis, the 

 French anatomist was quite correct in his general morphological statement, 

 although he was not legitimately entitled at the time to employ the illus- 

 tration. 



