~ 
1883. ] Especially those of the Limés. 509 
though greatly variable and complicated in their origin, have 
been beautifully explained by Rathke and his successors by ref- 
erence to a general plan of branchial arches, a plan nowhere com- 
pletely realized, but approximated more or less closely. 
If we, in like manner, go back to the primitive limb, we have, 
according to Gegenbauer, and others, a central stem along which 
are developed radiate elements at regular distances, each element 
arising at or near a joint. In the limbs of the higher vertebrates 
the number of rays is reduced, those on one side being entirely 
suppressed, 
A discussion of the subject would be foreign to the purpose of 
the present paper. I only wish to point out that the ramifica- 
tion of limb-arteries affords the theory some support. For each 
original ray would have its separate trunk, and at the convergence 
of the rays these would fall into an axis trunk. Suppress the 
tays of one side and a regular dichotomous division remains. 
Proceed farther and gradually suppress those of the other side 
and we might expect to find traces of those latest suppressed in 
small trunks supplying new structures which came to be formed, 
_ having as an indication of their radial character an origin not far 
removed from the point of segmentation of the limb. 
If this is a proper view the internal iliac and profunda femoris 
in the lower limb, the thyroid axis and superior profunda in the 
upper may be considered as arteries originally belonging to inde- 
pendent rays now aborted. Of the same category are the inter- 
osseous in the arm and the peroneal in the leg. 
The operation of this law, if it be such, is obscured in some 
cases by the formation of anastomoses crossing from one ray to 
another at the points of segmentation. Thus arise the palmar 
and plantar arches formed below the carpo-metacarpal and tarso- 
metatarsal joints. : 
It is also obscured by the operation of two laws derived from 
the centripetal development of the vascular system. The first of 
these may be called variability of convergence. If some cause » 
slightly diverts a forming trunk from its normal course, the devi- 
ation would increase in proportion as it approached the heart, the 
‘tunk would debouch at an unusual point and this would cause 
is known as an abnormal origin for the artery. 
€ convergence may be more or less than normal. If more, 
origin would be farther from the heart; if less, nearer. When 
Th 
the 
