69 



Thus the head consists of the three primitive pairs of cerebral 

 ganglia, arranged in a triangular form with the traces of the organs 

 of vision and hearing: the whole invested in a soft white integu- 

 ment. 



Immediately below the head the trunk swells out into a gently- 

 curved line, in which are seen by transmitted light, the paralleHines 

 (fig. II., 2), at regular and short intervals, indicating the points of di- 

 vision of the primitive notocord, into the several sets of vertebrae. 

 These transverse divisions are as yet equal throughout the whole 

 length of this primitive spinal column, which, after curving somewhat 

 abruptly forward at its extremity, ends in a narrow point or tail 

 (5). 



The little buds (3 and 4) which indicate the extremities are 

 already conspicuous, projecting from either side of the trunk; the 

 anterior pair, about one-third of a line in length, being more deve- 

 loped than the posterior pair. The latter are situated closely on 

 either side of the pointed extremity of the trunk, which projects be- 

 yond them, and thus renders them less conspicuous than the upper 

 pair. 



The trunk, therefore, here consists of the curved and primitive 

 spinal column, already showing the divisions or markings out of the 

 vertebrae, together with the little buds indicating the upper and lower 

 extremities. Posteriorly, and above and below, the trunk is gently 

 bent upon itself, and presents everywhere a smooth and curved out- 

 line, being covered in all parts by integument of a white colour, but 

 anteriorly the whole of the abdominal and thoracic cavities are per- 

 fectly open, these cavities being in fact not yet formed, or perhaps 

 only so slightly protected by integument that the mere act of open- 

 ing the sac of the amnion in which the foetus lies, and with which its 

 integument is closely connected, serves to break down any slight 

 covering which the trunk might have already received in this situa- 

 tion. 



In the present instance, the whole anterior part of the body is 

 thus open, from the head to the point of origin of the umbilical ves- 

 sels. The mouth is not yet formed, but a simple elongated opening, 

 beneath the head, consisting of two parallel folds of integument, 

 indicate the commencing formation of the naso-buccal fissure, which 

 itself is again transformed into the nose and mouth at a still later 

 period. 



On either side of this anterior fold or aperture are two minute 

 openings (fig. II., 8 and 9) in the neck, which may even be discovered 



