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CONTRIBUTIONS TO ZOOLOGICAL PATHOLOGY. 
mities terminate also in rounded points that articulate with the 
apices of the styloid appendages of the temporal bones. The 
entire bone is developed by five centres of ossification. Anteriorly 
it gives attachment to the base of the tongue ; posteriorly it is 
articulated to the anterior cornua of the thyroid cartilage, and su- 
periorly it is suspended to the temporal bones by means of their 
appendages. 
The thyroid cartilage is the largest of the cartilages of the 
larynx, and forms a kind of box for the reception and protection 
of the others. It consists of two lateral portions — the alae or 
wings — that meet in front at an acute angle, and form a large 
projection, the pomum adami in man, immediately behind the os 
hyoides and between the angles of the lower jaw. Each ala is 
of an oblong quadrilateral form : the external surface is convex 
and smooth, and presents along its superior part a ridge, oblique 
in its direction from above downwards and forwards, and giving 
attachment to the thyroideal portions of the sterno-hyo-thyroideus, 
the thyro-hyoideus, and the constrictor pharyngis posterior: a little 
in front of this ridge, and towards the anterior border of the cartilage, 
is a large foramen that transmits the deep branch of the anterior la- 
ryngeal nerve. The internal surface is concave, and along its mesial 
line gives attachment to the pedicle of the epiglottis and the chordae 
vocales. The anterior edges are more or less horizontal, and give 
off at their superior angles the anterior cornua, which articulate with 
the greater cornua of the os hyoides ; and along its entire margin 
is affixed the thyro-hyoid membrane. The posterior edge, along 
the mesial plane, is scooped out and concave, and when viewed 
in junction with the opposite ala, forms the crico -thyroid space 
in which the operation of laryngotomy is performed. Above, and 
behind this, the margin is convex, and overlaps the cricoid car- 
tilage, and its superior angle terminates in a rounded condyloid 
process, which articulates with the concavity on the side of the 
cricoid cartilage. 
The cricoid cartilage is a ring of cartilage contained within the 
thyroid, contracted below, forming the ring, and broad and ex- 
panded above, forming the body. Its external surface is very 
irregular. At the junction between the ring-like process and the 
body there is a large concavity for the reception of the correspond- 
ing articular process' of the thyroid cartilage. This cavity is 
covered with an articular cartilage, and lined with a synovial 
membrane. Along the superior, or pharyngeal surface of the 
body of the cartilage, there is a considerable elevation or ridge, 
giving attachment to the oesophagus and the posterior constrictors 
of the pharynx ; and on either side of this there is a large depres- 
sion that gives origin to the crico-arytenoideus posticus muscle. 
