42 C. W. M. Poynter 
all classes of mammals there is variation in the arrangement of 
branches from the arch in the individual species. No single 
species or genus shows a wide variation till primates are reached, 
and man seems to present as anomalous development all of the 
conditions encountered in other mammalia. I have already re- 
viewed, see page I1, the significance of the comparative anatomy, 
so it will only be necessary here to repeat that in citing under the 
various groups the animals presenting the same condition nor- 
mally it is done simply as a point of morphologic interest and 
not with the idea of suggesting an atavistic relationship. 
Some of the variations already included in the preceding sections 
will be repeated here; this applies particularly to I], D, 1. This 
seems necessary because the basis of classification for this section 
is different than for the preceding and it is desirable to present 
together all of the examples of a given type of variation. 
A. Irregularities in the Branches from the Ascending Aorta 
1. Irregularities of the Coronary Arteries—The coronary ar- 
teries exhibit several irregularities ; of these the most frequent is 
the presence of one or more accessory arteries. Symmers (1907) 
reported these present in 40 percent of cases and that they were 
more frequently present on the right side. This is greatly in 
excess of the percentage present in the series reported by Hal- 
bertsma (1863) and Banchi (1904) ; the latter finds that when a 
third branch is present it is generally a branch of the right coro- 
nary, which has a separate origin from the aorta. In a hundred 
observations I have found in two instances that the area usually 
supplied by the right coronary was furnished by two short trunks 
direct from the aorta; this confirms Banchi’s observation. 
One artery may be absent and in that case the other artery sup- 
plies the entire heart. 
The arteries, one or both, may arise higher than normal from 
the aorta, as in the cases reported by Farre (1814), Mayer 
(1827), Hyrtl (1841) and Chevers (1851). 
Arteries multiple: Morgagni (1761), Meckel (1817), Halbertsma (1863), 
Krause (1865), Brooks (1885) from pulmonary, Hepburn (1886), Banchi 
(1904-7), Symmers (1907). 
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