OF ECHIDNA AND ORNITHORHYNCHUS. 5 
over the cricoid cartilage, the external fibres, diverging as they go, are inserted into 
the external angle, the dorsal surface and its posterior border of the arytenoid. 
The remaining fibres, including most of those from the cricoid origin and a portion 
also of those from the thyroid cornua, are inserted into the anterior procricoid. 
A small but distinct aryteno-procricoid (a.p.) lies concealed for the most part 
below the fibres of the posterior thyro-arytenoid, and, owing to the great develop- 
ment of the procricoid cartilage, takes the place of the more usual inter-arytenoid 
muscle. 
The lateral thyro-arytenoid and lateral crico-arytenoid form a continuous sheet 
of muscle, called by Dusots thyreo-ary-cricoideus, and represent the constrictor of 
the larynx. The anterior fibres arise from the inner aspect of the body of the thyroid, 
and the adjacent portion of its inferior cornua; a few fibres arise more posteriorly 
from a line on the lateral and ventral aspect of the cricoid, close to its anterior 
border. Converging from these two origins, the muscle is inserted into the external 
border and outer side of the arytenoid cartilage. This muscle is found in both 
Echidna and Ornithorhynchus, and in both a few of the anterior fibres pass into the 
epiglottis, forming an aryteno-epiglottidean muscle. 
Of these intrinsic muscles all, except the aryteno-procricoid, were recognized in 
Ornithorhynchus. 
It will be seen that the above account, so far as it goes, gives abundant support 
to Dusors’ theory based upon one of the two types here considered. The two pair _ 
of hyoid and two pair of thyroid cornua form together a system of four post- 
mandibular visceral arches; and the remarkable series of inter-thyroid, thyro-hyoid, 
and inter-hyoid muscles symmetrically connect them. 
The simple condition of the constrictor and dilator muscles of the larynx is 
also noteworthy. 
As regards the skeletal differences in this region between the two types, the 
greater size and ossification of the body of the hyoid, the better developed body of 
the thyroid, the robuster anterior hyoid cornua, the incomplete cricoid, and the 
better developed (?) procricoidea mark out Echidna as the more primitive form of 
the two, in respect to this as to so many other anatomical regions. 
A point of considerable interest, which appears to have remained unnoticed, 
may be mentioned here. By means of an extraordinary prolongation of the soft 
palate, the elongated pharynx is divided into two passages. The dorsal one, a 
continuation of the posterior nares, is directly continuous with the gullet. The 
ventral one, continuous with the mouth, seems in a state of rest to be shut off from 
the other posteriorly, the broad semicircular epiglottis standing upright and coming 
in contact by its margin with the crescentic thickened posterior margin of the soft 
palate. From such a condition as this the transition is equally easy to the ordinary 
condition of the epiglottis and to the intranarial epiglottis of young Marsupials, of 
