[1001 mammalian and bird, embryos are of importance in showing 

 that the caudal filament is of general occurrence and not a 

 peculiarity of the hnman tail. x\gain, the occurrence of 

 spinal nerves and ganglia in a number of the coccygeal seg- 

 ments, as shown by Fol,*^ Phisalix and Keibel, the continu- 

 ation of the aorta and vena cava into the caudal filament, 

 together with the presence of segmental arteries and the 

 hypapophyses or rudimentary haemal arches in all of the 

 coccygeal segments as described in the present paper, show 

 that the caudal region of the human embryo resembles that 

 of other mammalian embryos in all respects except in size and 

 in the number of its segments. 



Concerning the regressive development of the tail consid- 

 erable difference of opinion has been expressed. Eosenberg, 

 who holds that, strictly speaking, the caudal rudiment in man 

 is not the homologue of the tail of other animals, but is the 

 result of a precocious growth of the medullary cord,^* con- 

 siders that the appendage disappears in consequence of the 

 increase in volume of that end of the embryonic body and 

 not through absorption. His,^' in supporting Eosenberg, 

 makes the statement that no reduction in the number of seg- 

 ments takes place during the development of the human 

 embryo, but that the regressive changes are confined to the 

 caudal filament; this view is confirmed in the agreement with 

 Ecker. On the other hand, Fol and Phisalix find thirty-eight 

 segments in embryos of 8-10 mm., with indications that sev- 



3"^ H. Fol : Sur la queue de rembryon humain. Comptes Rendus, T. 

 100, Paris, 1885. 



33 C. Phisalix: Etude d'un embryon humain de 10 millimetres. Ar- 

 chives de Zool. Exp. et Gen. 11^^ S., T. vi, 1888. 



3^ E. Rosenberg: Ueber die Entwickelung der Wirbelsaule und das 

 centrale carpi des Menschen. Morphol. Jahrb., Bd. i, 1876. "... dass 

 die Gestaltung des hinteren Leibesendes ebenfalls von dem Medulla- 

 rohr derart beeinflusst wird, dass letzteres, indem es in seinem Langen- 

 wachsthum dem der anderen, un der Zusammensetzung des hinteren 

 Leibesendes Theilhabenden Bestandtheile vorauseilt, an demselben 

 einen Vorsprung erzeugt. ..." p. 128. 



35 «' Es werden demnach beim menschlichen Embryo keine iiberzahligen 

 zur Riickbildung bestimmten Segmente angelegt." Anatomic men- 

 schlicher Embryonen, i, p. 92. 



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