70 



by the unassisted eye. These are evidently the remains of the so- 

 called branchial openings or fissures, of which the upper pair (8) 

 was probably destined to remain permanent, and to become the ex- 

 ternal meatus ; the lower (9) would probably have soon been ob- 

 literated. 



The only viscera which can be discovered are a small mass (10) 

 on the right side, on a level with the anterior extremities, which is 

 generally termed the hepatic mass, and indicates the future liver ; 

 and at the same height on the left side is seen a curved vessel or 

 hollow organ (fig. III., 12, 13 and 14), divided into three parts, upon 

 the use of which there can, I think, be little doubt. All analogy and 

 all reasoning as to the organs which would be requisite to carry on life 

 at this stage of embryo existence, would, I think, point to this as one 

 connected with the circulation, the establishment of which is essen- 

 tial at this stage, rather than with digestion, for which there is no 

 need. I shall, therefore, be justified in regarding this as the primi- 

 tive condition of the heart, and shall presently revert to this part of 

 the subject, for the purpose of contrasting the development of the 

 organ at this period with two other examples, at a somewhat later 

 stage. 



With the exception of the organs just described, there appear to 

 exist no others. A slight indication, however, of two linear-shaped 

 bodies is discoverable along the back of the open abdominal cavity, 

 and these, both on account of their situation and form, may be as- 

 sumed to be the incipient Corpora Wolffiana, the transitional repre- 

 sentatives of the future kidneys and testes or ovaria. 



Lastly, immediately above the curved extremity of the trunk, the 

 minute umbilical chord (15) is seen blending itself with the cho- 

 rion, and surrounded by the amnion, but the course of the vessels 

 could not be traced. There was no indication of the presence of 

 either an umbilical vesicle or of an allantois in this embryo. 



I have now only to offer a few observations on the development of 

 the heart to which I have just adverted. I have described this organ, 

 in the present case, as presenting the appearance of an elongated 

 vessel curved upon itself and exhibiting three divisions or chambers, 

 representing the single auricle (fig. IV., a), ventricle (b), and bulbus 

 arteriosus (c), which compose the heart of the lowest class of verte- 

 brate animals, or that of fishes. The two latter chambers have thick 

 and fleshy former, the latter is thin and membranous ; the whole con- 

 stituting an organ closely resembling that which we observe as a 



