2 MARY L. WALKER ON THE LARYNX AND HYOID 
truncated to form somewhat large concave facets fur the attachment of the posterior 
cornua. The anterior cornua consist (so far as they could be examined) of three 
ossified segments, but they had been cut short, and their cranial extremities could 
not be studied. The first or proximal segment passes almost directly forwards. 
The posterior cornua passes outwards and backwards from its articulation with the 
body of the hyoid. It forms a broad osseous plate, which runs parallel for rather 
more than half its length with the anterior portion of the thyroid, and then more 
posteriorly becoming cartilaginous, fuses with it. From the anterior margin of 
the cornua a rounded process projects forwards, whose outer edge slopes directly 
backwards, to be continuous with the outer margin of the anterior thyroid horn. 
In Ornithorhynchus, the body of the hyoid is much smaller, and transversely 
fusiform. The articular surfaces for the cornua are not well defined upon it, and, 
owing to its small size, the anterior and posterior cornua articulate with one another 
outside its lateral angles to a greater extent than with it. The anterior cornua are 
slender. Their proximal segments pass forwards parallel with one another, and are 
slightly ossified ; distally the cornua curve outwards and backwards, and are 
unossified. The posterior cornua pass outwards and backwards, as rather broad 
strips of imperfectly ossified cartilage: for two-thirds of their length a wide space 
separates them from the anterior edge of the thyroids, but close to this origin from 
the body of the horn they are for a short space in contact with the thyroids, with 
which they again come into relation at their outer ends, an oblique line of fissure 
in the cartilage separating the one from the other. At the antero-lateral angle, 
a process more square and definite in outline than in Echidna passes forward from 
the posterior cornua. 
The Thyroid Cartilages. 
It is impossible to doubt that the elements above described represent the body 
or copula in the two pair of.cornua of the hyoid in higher forms; and it is equally 
impossible to avoid recognizing, as Dupots has already shown, that the structures 
next to be described correspond to the thyroid cartilage of more ordinary types. 
In Echidna, a median cartilaginous element, rectangular, narrow, and elongated 
from before backwards, articulates with the body of the hyoid. In relation with it 
are two pair of cornua. Together, these cornua with their median piece or copula 
represent the thyroid cartilage. The anterior cornua articulate with the copula to a 
very slight extent; to a greater extent they come in contact with the posterior 
margin of the body of the hyvid. Passing outwards and broadening as they go, 
they lie parallel with and separate from the posterior hyoid cornua for about half 
their length ; after which they fuse with the latter, as has been already described, 
and extend backwards till each terminates in two short processes at its posterior 
angle. ‘The posterior cornua are separate from and overlapped by the anterior. 
