4 MARY L. WALKER ON THE LARYNX AND HYOID 
anterior thyroid cornua was in closer relation with the posterior arch of the 
hyoid. Possibly a sexual character may be at the bottom of these differences, in 
all of which Duzots’ specimen approaches our figure of Echidna. 
Muscles connected with the Hyoid. 
For the reasons already mentioned, the extrinsic muscles in Echidna and the 
muscles generally in Ornithorhynchus were imperfectly studied. It was noted 
that the sterno-hyoid muscle was wanting in Ornithorhynchus, a fact to which 
Dvusots has called attention. The sterno-hyoid and sterno-thyroid are both present 
in Kchidna. 
The inter-hyoid (i.h.) in Echidna is a large thick muscle, composed of several 
layers. It arises from the outer angle and adjacent portion of the anterior border 
of the posterior cornua of the hyoid, and is inserted into the posterior border of the 
anterior cornua in its two inferior segments. It is present in Ornithorhynchus. 
The inter-thyroid (i.th.) consists of short fibres passing obliquely forwards 
between the cornua of the thyroid. The more internal (median) fibres pass 
obliquely outwards, the more external slightly inwards. In Ornithorhynchus the 
muscle is present, but very small. 
The thyro-hyoid (t.h.) is similarly placed between the anterior cornua of the 
thyroid and the posterior cornua of the hyoid. Its fibres are very short, and are, 
to a great extent, replaced by ligament. 
In Ornithorhynchus the thyro-hyoid is better developed, and in this animal 
we also noticed a curious slender strip of muscle passing directly from the external 
process of the anterior thyroid arch to the outer part of the anterior arch of the 
hyoid. 
Intrinsic Muscles of the Laryna. 
The crico-thyroid (c.t.) in Echidna appears to arise from the free end of the first 
ring of the trachea. It unites partly with its fellow of the opposite side in an 
aponeurosis, which plays over the anterior part of the cricoid cartilage, and is in 
part inserted into the internal end and adjacent lower border of the posterior 
thyroid cornua. The nerve to this muscle appeared to be a branch of the recurrent 
laryngeal. According to Dusors the crico-thyroid is absent in Ornithorhynchus, 
but in our specimen there was a small muscle apparently corresponding to the 
description given above, but much smaller. 
The posterior thyro-arytenoid and crico-arytenoid (p.) together form one muscle, 
called by Dusots kerato-crico-arytenoideus, and represent the dilator of the larynx. 
The fibres arise from the extremity of the posterior cornua of the thyroid, and form 
the edge of the great notch on the dorsal aspect of the cricoid. Passing forwards 
