_Appendix_.--Since writing the above, I have received an answer to a letter I addressed to my friend, John Goodsir, Esq., Professor of Anatomy in the University of Edinburgh. The request contained in my letter to Mr. Goodsir was, to examine for me the skeleton of a foetal _Mysticetus_ now in the University Museum. The foetus from which this skeleton was prepared was removed from the uterus of the mother, killed in the North Seas by the seamen of a whaling ship, by one of my former students, Mr. R. Auld, who presented the specimen to me. The point at issue was the composition of the cervical vertebrae in the true or Greenland Whale, the _Balaena Mysticetus_. M. Van Beneden, to whose memoir I have referred in the commencement of this, says, on the authority of Eschricht, that at no age whatever do we find in true Whales (meaning, I presume, the _Mysticetus borealis_ and _australis_) any distinct vertebrae in the cervical region, as in other mammals. A fusion of all into one bone or cartilage seems to take place even in the youngest foetus. Now, I had enjoyed the rare opportunity of dissecting the foetus of the _Mysticetus_, and I knew that the skeleton, prepared with the greatest care, was still preserved in the Museum of the University of Edinburgh. I wrote to Mr. Goodsir to re-examine this point for me, for I did not find in my notes any confirmation of the observations of Eschricht. Mr. Goodsir's reply to my note is as follows:-- "University, Edinburgh, Sept. 30, 1857. "MY DEAR SIR, "In the skeleton of the foetal _Mysticetus_ now in the University Museum, the bodies of the axis and atlas have shrivelled up together, having evidently consisted of cartilage only; but the bodies of the five posterior cervical vertebrae are beautifully distinct, having well-formed osseous centres, which give them more of the configuration of the succeeding vertebral bodies than they present in their compressed form in the adult. "The neural arches in the cervical region of this skeleton are five in number; the two anterior, which are distinctly those of the atlas and axis, have an osseous nodule on each side, where the transverse processes pass off. The third arch belongs to the third vertebra, the fourth and fifth to the sixth and seventh. These three arches are cartilaginous, and present no osseous centres. It is impossible to determine from the preparation whether the arches of the fourth and fifth vertebrae had been cut away in dissecting the parts, or whether they have shrivelled up in drying; but as the skeleton was very carefully prepared, and as these two arches are deficient (at least laterally) in the adult _Mysticetus_, I presume that the cartilaginous matrices were at least extremely delicate in the foetus.