470 BUMPUS. [VoL. XII. 
Reptilien, Vogel und Sauger, und sie gelten auch ebenso gut 
bei allen Vertebraten fiir die hintere Extremitat —es handelt 
sich um ein festes, die ganze Vertebraten-Reihe beherrschendes 
Gesetz, dass der Anstoss zur Entwicklung des Gliedmassen- 
skeletes stets von der Peripherie ausgeht, und dass sich die 
centralen (Giirtel-) Theile erst secundar unter dem formativen 
Einfluss der freien Gliedmasse entwickeln.”’ 
One of course feels some regret that there is not a suffi- 
cient number of examples of backward homeeosis for the basing 
of a conclusion in regard to the association of backward homee- 
osis with trunk elongation. The only specimen which shows 
this unusual homeeotic tendency is No. 62, and on a reference 
to Plate C it will be seen that its XIX intervertebral septum 
is located on the mean abscissa of 33%. 
Section VI. 
Are variations in the relative position of the pectoral arch 
associated with variations in the relative position of the pelvic 
arch? 
The pectoral arch, located near the anterior end of the body 
and closely associated with the head and visceral skeleton, 
would be expected a priorz to show a lesser amplitude of varia- 
tion in respect to the segments of the vertebral axis than is 
shown by the pelvic arch. In front of it are only three verte- 
bree, and the limits of vertebral elasticity, if I may use the term, 
are correspondingly restricted. 
On the other hand, the shoulder girdle is not articulated to 
any one vertebra, and those intimate relations between bones 
which we have been taught are so potent in determining their 
position and character, do not here exist, and were it not for 
the tensile influence of the myotomes the enclosed vertebrze 
might slide back and forth through the arch ad /zbztum. 
Since the girdle thus lies imbedded only in muscle tissue, 
its normal position in relation to the embraced vertebrz is 
rather difficult to determine from specimens which have been 
killed without special care. My observations, however, con- 
vince me that the halves of the arch do not always occupy the 
same position with regard to the vertebral segments. 
