592 
CONTRIBUTIONS TO ZOOLOGICAL ANATOMY. 
Dissection. — Remove all the former group of muscles from the 
os hyoides, dissect away the vessels and nerves from the side of 
the pharynx, and draw downwards and forwards the bone with a 
pair of hooks, and both these muscles will be exposed, — the pos- 
terior muscle on the side of the bone, and the anterior between 
the lesser cornua and the convex surface of the epiglottis. 
The Anterior or transverse chondro-hyoideus muscle is situated 
along the superior surface of the body of the os hyoides, and 
between the anterior or lesser cornua. It is formed of a rounded 
and firm band of fibres of a semi-oval form, convex towards the 
base of the tongue, and concave upwards and backwards to the 
epiglottis, from which latter, however, it is separated by the 
hyoideal insertions of the genio -hyo-glossi muscles. 
Its fibres arise from the inner surface of the anterior cornu of 
one side, and arch slightly across to the corresponding surface of 
the opposite cornu. Anteriorly it is covered by the superior or 
posterior margins of the hyo-glossi, and the inferior margins of the 
genio -hyo-glossi muscles; and posteriorly, the arched hyoideal 
fibres of the latter muscles and some loose fat intervene between it 
and the epiglottic fibro -cartilage. By its action it approximates 
the anterior cornua of the os hyoides, and by this means compress- 
ing the base of the tongue upwards and backwards, causes the 
contents of the numerous mucous follicles at its base to become 
emptied of their contents during the passage of the bolus of food 
over the epiglottis. By this action it also aids the palato-pharyn- 
geus muscle in constricting the isthmus faucium at its base, and 
serving the purpose, in man, of the palato-glossus, which latter 
muscle is absent in the quadrupeds. The muscle, however, has no 
influence over the position of the epiglottis, or the state of the 
rima glottidis. 
The Posterior chondro-hyoideus is placed behind the former 
muscle, in the angle between the anterior and posterior cornua. It 
is of an irregular triangular form, with two of its sides attached ; 
one to the anterior edge of the posterior cornu, immediately within 
the origin of the hyo-glossus, and before that of the constrictor 
pharyngis medius ; and the other, its insertion , is attached to the 
whole of the posterior edge of the anterior cornu. Externally it 
is covered by the inferior extremity of the styloid appendage 
of the temporal bone, the hyo-glossus, and the tendons of the 
stylo-hyoideus and digastric muscles ; and internally it lies on the 
genio-hyo-glossus and the constrictor pharyngis anterior. In the 
combined actions of both muscles they draw backwards and fix 
the anterior cornua to the body and posterior cornua of the os 
hyoides, and, thus fixing the extremities of the styloid appendages 
of the temporal bones to the anterior cornua, enables the muscles 
