THE HYOID APPARATUS 197 



sion for the insertion of the pterygoideus interniis muscle. The 

 area occupied by the pterygoideus internus is separated by a low 

 ridge from a more dorsally placed superior depression for the 

 pterygoideus externus muscle. A somewhat similar depression, 

 termed the masseteric fossa, occupies the lateral surface of the 

 angle, its raised ventral margin terminating posteriorly in the 

 masseteric tuberosity (tuberositas masseterica). The articular 

 portion or head of the mandible is greatly elongated in the 

 anteroposterior direction in accordance with the anteroposterior 

 action of the lower jaw, this feature being one which is of general 

 occurrence in the rodent order, and more fully expressed in the 

 great extension forward and backward of the attachment areas 

 of the muscles of mastication. The connection of the articulating 

 portion with the condyloid process, the so-called neck of the 

 mandible (collum mandibulae), is a thin plate of bone, the anterior 

 and posterior margins of which are barely notched by the anterior 

 and posterior mandibular incisures. Connecting the anterior 

 incisure with the rim of the alveolus of the last cheek-tooth there 

 is a deep groove, the sulcus ascendens, the lateral margin of which 

 is formed by the reduced coronoid process (processus coronoideus). 

 Its low medial margin is formed by a bony stay which extends 

 to the medial surface of the horizontal portion opposite the last 

 cheek-tooth and is continued forward into the mylohyoid line. The 

 sulcus ascendens lodges in the natural condition the insertion 

 portion of the greatly reduced temporalis muscle. 



The Hyoid Apparatus 

 The hyoid bone (os hyoideum) (Fig. 91) is a stout, somewhat 

 wedge-shaped bone lying in front of the larynx and between the 

 angles of the mandible. Its ventral portion is connected with the 

 thyreoid cartilage of the larynx by the median hyothyreoid liga- 

 ment. With its lateral portion are articulated two independent 

 elements, termed the lesser and greater cornua. The lesser 

 cornu (cornu minus) is a small, partly cartilaginous structure, 

 attached to the anterodorsal angle of the hyoid, and connected 

 through the stylohyoideus minor muscle with the jugular process 

 of the skull. The muscle tendon contains, near the jugular process 

 a small ossification representing a detached styloid process. The 



