579 
ing 1) the origin of the intrinsic laryngeal ring, and 2) the origin of 
the extrinsic transverse muscles. 
1. Origin of the laryngeal ring. 
The fact that in its simplest form this system consists of a ring 
surrounding the mouth of the air passages, suggests as the most plau- 
sible theory that we have here merely a continuation of the 
ring-musculature of the alimentary canal which the 
developing respiratory tract carried with it when it 
arese as a diverticulum from the former. That at first its 
action was simply that of a sphincter, and that it secondarily obtained 
_ relations with the Arytaenoids, I have already stated in the paper 
upon Siren above referred to. If the question of striation or non- 
striation should be felt as an objection by any one, we have an exact 
parallel in the pharyngeal constrictors of the Mammalia which are 
clearly conceded to have differentiated from the muscular layer of the 
upper portion of the oesophagus. We have seen the capability of 
differentiation of this ring illustrated in the class of Amphibia, and it 
would be no difficult task to follow out the homologies in the higher 
vertebrates. 
2. Origin of the extrinsic system. 
For this I have as yet only a partial solution, which may be seen 
by a comparison of the two diagrams, figs. 2 and 3. The first of 
these is an attempt to represent, in diagrammatic form, the super- 
ficial muscles, and their relation to the segmental nerves and visceral 
arches; while the second represents the actual relationship of parts 
in the lower Urodeles, giving the most probable homologies. For the 
most of these I do not claim originality but have tabulated the results 
of VETTER and others as I have understood them !). 
According to the last named author, the cephalic and branchial 
regions of the Selachians are covered by an extensive system of 
muscles referred to by him as the superficial constrictors. These are 
divided into dorsal and ventral segments, and bear definite orderly 
relations to the different gill arches and segmental nerves. This is 
shown in fig. 2. Comparing this with the Urodele, fig. 3, it will be 
observed that the dorsal segments are still distinguishable, the second 
alone (digastricus) having changed its insertion, and that the seventh 
dorsal segment corresponds exactly in origin, insertion, innervation 
and relation to the branchial arch (= Arytaenoid) with the trans- 
1) B. Verrer, Untersuch. zur vergl. Anat. d. Kiemen- u. Kiefermus- 
kulatur d. Fische. Jenaische Zeitschrift, Bd. VIII u. XII. 
