[ 1% 
Ill. On the Larynx and Hyoid of Echidna and Ornithorhynchus. 
By Mary L. Waker, University College, Dundee. 
Great interest attaches to the monotreme larynx, not only on account of its obvious 
peculiarities, but also because it forms the basis of Dusots’ remarkable theory of 
the morphology of the thyroid cartilage. According to Dubois the mammalian 
larynx is a composite structure. While the cricoid and arytaenoids are derived 
from the trachea, the thyroid cartilage is a derivation of the visceral skeleton, and is 
constituted out of two pair of post-hyoid visceral arches, z.e., the fourth and fifth 
visceral arches, with their copula. In Amphibia and Reptilia these have not yet 
entered into the composition of the larynx at all: in Ornithorhynchus they still 
remain as separate arches: in higher mammalia the thyroid gives frequent indica- 
tions of its primitive constitution, as for instance in the bifurcation dorsally into 
anterior and posterior cornua, or in the presence of a thyroid foramen which is a 
relic of the original separation of the two arches. 
Of the few available descriptions, the older ones, for instance that in Topp’s 
Cyclopzedia, are pnsatisiactory and inadequate. Of more recent accounts, the most 
complete 1 is Dusots’ paper,* dealing with the larynx of Ornithorhynchus, and it is 
in points at variance with the account given by WiepERSHEIMt of the larynx of | 
Echidna. 
Our specimen of Ornithorhynchus was not in very good preservation, and the 
laryngeal muscles were imperfectly studied. Rough sketches and notes were, how- 
ever, taken of them some time ago, when the larynx was prepared for our Museum. 
The Echidna’s larynx was furnished us by Professor CHaRLEs Stewart, and the 
dissected preparation is now in the Hunterian Museum. It had been removed from 
the body, together with a portion of the pharynx, and accordingly the extrinsic 
laryngeal and the pharyngeal muscles could not be properly investigated. 
The Hyoid Bone. 
In Echidna and Ornithorhynchus, the hyoid consists of a body and two pair of 
arches or cornua, which remain permanently separate from it. 
In Echidna, the body of the hyoid is well ossified, large, and transversely 
elongated : its anterior margin presents two concave facets, separated by an inter- 
space, for articulation with the anterior cornua; the postero-lateral angles are 
* Duos, Zur Morphologie des Larynx. Anat. Anzeiger, I. Jahrg., Nos. 8, 9, Sept. Oct., 1886. 
+ Lehrbuch d. vergl. Anatomie, Ist edit., p. 658. 
