Genekal Considerations. 



[1001 



Ecker and His were the first to give detailed descrip- 

 tions of the caudal region of the human embryo. Their con- 

 clusions regarding its definition and ultimate development 

 may be taken as the starting point in the discussion of the 

 subject. The agreement reached by Ecker and His may be 

 rendered in part as follows:'* (1) The term "tail" may be 

 applied only to that portion of the embryo which projects 

 free beyond the cloaca. (2) The tail consists of a portion 

 containing vertebras and a portion without vertebrge (caudal 

 filament). The latter contains only notochord and medullary 

 cord. (3) Only the non-vertebral portion atrophies. The 

 vertebral portion remains for some time as the coccygeal 

 prominence {Steisshocker), which, however, gradually disap- 

 pears in consequence of the increase in the curvature of the 

 sacrum and coccyx, and of the progressive development of 

 the pelvic girdle and its musculature. 



Two matters which have a bearing upon the morphological 

 significance of the persisting caudal appendages in man are 

 brought up in the above for consideration. The one concerns 

 the structure of the tail in the human embryo in comparison 

 with the tail in lower forms; the other is the nature and 

 amount of regressive change which takes place in the human 

 tail during development. 



Eegarding the first, Keibel discovered an additional fact 

 of importance in the presence of a post-anal gut in the human 

 embryo. Braun's " observations on the caudal filament of 



2^ A. Ecker: Archiv f. Anthropol., Bd. xii, 1880. 



A. Ecker: Besitzt der menschliche Embryo einen Schwanz ? Archiv 

 f. Anat. u. Physiol, anat. Abtheil., 1880. 



28 W. His : Anatomic menschlicher Embryonen, I, Leipzig, 1880. 



W. His : Ueber den Schwanztheil des menschlichen Embryo. Archiv 

 f. Anat. u. Physiol, anat. Abtheil., 1880. 



29 A. Ecker: Replik nnd compromissitze nebst Schlusserkarung von 

 W. His. Archiv f. Anat. u. Physiol, anat. Abtheil., 1880. 



30 Fr. Keibel : Ueber den Schwanz des menschlichen Embryo. Archiv 

 f. Anat. u. Physiol, anat. Abthiel., 1891. 



31 M. Braun : Entwicklungsvorgange am Schwanzende bei einigen 

 Saugethieren mit Beriicksichtigung der Verhaltnisse beim Menscheu. 

 Archiv f. Anat. u. Phys. anat. Abtheil., 1882. 



(13) 



