782 SUMMARY OF CURRENT RESEARCHES RELATING TO 



upwards the human embryo is endowed with this organ, for at this 

 epoch the coccygeal vertebrae occupy the axis of a cylindro-conical 

 appendage, which is very apparent, and which issues from the pos- 

 terior extremity of the trunk. If with His we take the position of 

 the anus for a guide, the tail will be shorter, but is still very 

 conspicuous, especially at the age of five to sis weeks. 



But it is generally admitted as absolutely demonstrated that this 

 caudal appendage of the human embryo never contains any other 

 vertebrae than those found in the coccyx of the adult. Ecker, who 

 gives, in full conviction, the name of tail to the posterior extremity 

 of the human embryo, has declared that he has never met with any 

 supernumerary vertebrae. This author has even studied the well- 

 developed tail of a human embryo 9 mm. in length, and he describes 

 and figures all the terminal part as consisting of an amorphous blas- 

 teme. His, however, detects here a prolongation of the dorsal cord 

 and of the spinal marrow, but no segmentation. Both these autho- 

 rities admit that beyond the thirty-third or thirty-fourth vertebra 

 there is no further portion of the skeleton. 



On this point the researches of Prof, Fol have led him to a result 

 diametrically opposite to that of his predecessors. The error of His 

 is due to the circumstance that the oldest embryos which he has 

 examined, those of 7 mm., have exactly thirty-four myomeres, that is 

 to say, thirty-three vertebrae ; and he admits, without any further 

 proof, that this was their ultimate condition. 



Prof. Fol gives a summary of his anatomical study of a human 

 embryo of 5 • 6 mm., i. e. of twenty-five days old. This embryo has as 

 yet only thirty-three somites, representing thirty-two vertebrae. There 

 is, therefore, an increase in number in the fourth week. This fact 

 led Prof, Fol to examine if the number did not go on increasing 

 during the fifth week, and his expectation was not disappointed. The 

 human embryo of from 9 to 10 mm., the age when the tail attains its 

 greatest prominence, possesses a greater number of vertebrse than the 

 adult. 



Two embryos of the finest appearance, and perfectly fresh when sent 

 to the author, were first photographed and then cut into sections. The 

 series of sections are irreproachable, and one of the two, comprising 

 320 sections, has been most carefully drawn in the camera lucida in 

 its entirety. On comparing these 320 figures it is easy to count, 

 without any chance of error — (1) the rachidian ganglia; (2) the 

 myomeres ; (8) the nascent cartilages of the bodies of the vertebrae. 

 These three enumerations check and confirm each other, since they 

 all three give the same result ; the human embryo of 8 mm. has thirty- 

 eight vertebrse. 



This result is further confirmed by an examination of the photo- 

 graphs of the recent parts, since we readily distinguish thirty-five 

 myomeres, and besides a region occupying the external fourth part of 

 the tail where the demarcations are no longer visible through the 

 skin. But the sections show us that in this last quarter, contrary to 

 the opinion of Ecker and His, the mesoderm is most distinctly divided 

 into a double range of somites extending to the very tip of the tail, 



