10 
Proceedings of the Royal Society 
that the. sinus rhomboidalis in the medulla oblongata, the fourth 
ventricle in fact, was the position of the primitive mouth. This 
view he has also since given up. The hypothesis was discussed by 
Balfour in his monograph on the development of Elasmobranchs.* 
It is an astonishing fact that, until the publication of Sedgwick’s 
paper, morphologists had never fully grasped the significance of the 
development of the central nervous system in Vertebrates. Sedgwick 
has pointed out that the interior surface of the lining canal is part 
of the original dorsal surface of the body — that is to say, the condi- 
tion through which an Elasmobranch or Amphibian embryo passes, 
in which the nervous system is a double cord of thickened epiblast, 
widening out anteriorly into a plate, was the permanent condition of 
the Vertebrate ancestor. Sedgwick has not followed out this fact 
to its ultimate consequences. He has been misled by his desire 
to consider the present mouth and anus as identical with the original 
structures. At the meeting of the British Association at York in 
1881, Sir Richard Owen, in his address to the Department of 
Anatomy and Physiology of Section D, embraced the Dohrnian 
view of the homologies of Vertebrates and Invertebrates, and 
announced as a new hypothesis that the original oesophagus was 
represented by what he called the conario-hypophysial bract — that 
is, that the oesophagus originally passed from the hypophysis to the 
pineal gland. This was very much the same as Dohrn’s first view 
before 1875, which had to be abandoned. The reasons why it is 
* Professor Turner has kindly pointed out to me that John Goodsir, in a 
paper published in the second volume of his Anatomical Memoirs , Edinburgh, 
1868, speaks of a view he once held concerning the Vertebrate primitive 
mouth, which is similar to the view once held by Dohrn, as mentioned above. 
Goodsir’ s view, originally published in the Edinburgh Philosophical Journal in 
1857, was that the primitive oesophagus passed through the pituitary body, 
infundibulum, and third ventricle, and opened at the roof of the fourth ven- 
tricle behind the cerebellum. This theory, therefore, was a combination of 
the views which have since that time been successively favoured by Dohrn, 
and is anterior in date to any publications on the subject by Dohrn, Owen, or 
any others. Goodsir, in the paper I refer to, only mentions his theory to say 
that he abandoned it, because Reichert had shown that the pituitary body does 
not perforate the skull in the embryo. We know now that this reason for 
abandoning the theory does not exist. Goodsir completely agreed with Geoffrey 
St Hilaire’s view concerning the reversed positions in Vertebrate and Annelid 
or Crustacean, and also recognised that the dorsal blood-vessel in the latter 
was homologous -with the subintestinal vessel and heart in the Vertebrate. — 
Note added Jan. 28, 1885. 
