METAMERIC SEGMENTATION AND HOMOLOGY. 
241 
As in the case of the limbs, the theories of intercalation or 
redivision fail utterly when applied to the occipital condyles. 
The segmental homology of the condyles cannot be saved by 
such means without sacrificing the homology of other struc- 
tures of equal importance. 
Turning- now from these general considerations to the 
comparison of the condyles in the Ampliibiaand Amniota (15). 
There appear to be not more than three mesoblastic segments 
between the occipital condyle and the auditory capsule 
in the amphibian, and not less than five in the amniote.^ If 
the condyle is on the same segment in the two groups, two 
segments must have disappeared in Amphibia. These cannot 
have vanished at the front end of the series, as already 
pointed out above, unless the glosso-pharyngeal and vagus 
nerves, etc., are new in the amphibian — not homologous with 
those of the amniote — a supposition which is obviously not 
admissible. There is absolutely no evidence in embryology 
that the segments have disappeared between the vagus and 
the condyle ; but for the sake of argument let us suppose 
that they have. Does this help us out of our difficulties? 
Certainly not ! On the contrary it lands us in a worse position 
than before. For it must then be supposed that the fourth 
branchial slit of the amphibian corresponds to a sixth of the 
amniote, and the whole homology of the branchial arches and 
other connected structures is upset. And we are further met 
with an insuperable difficulty concerning the hypoglossal 
^ The results of most authors who have studied the composition of 
the occipital region of the Amniota are remarkably uniform. YTm 
Bemmelen (3), Corning (6) and Sewertzolf (19) in reptiles, Froriep (7), 
Belogolowy (2), in birds, find four myotonies in the einluyo. The first 
is quite vestigial and belongs to the second meta-otic somite, since the first 
somite corresponding to the glosso-pharyngeal nerve is niuchl reduced 
and never forms muscle (see Diagram 6). In mammals there appear to 
be also five somites and three distinct myotomes (Froriep (8) and others). 
A varying number of ventral nerve-roots join to form the hypoglossal. 
The first spinal (or post-occipital) still contributes to it in the reptiles and 
birds, but in the mammalia the hypoglossal roots are entirely 
intra-cranial. 
