DISSECTION OF THE HEAD AND NECK. 213 



-Directions.— B,emo-ve the larynx by cutting across the remaining 

 great cornu of the hyoid bone, and the root of the tongue in front of 

 the glossal (spur) process. Cut away the remains of the pharyngeal 

 muscles ; and, after examining the articulations of the hyoid bone, set 

 the larynx (and the attached hyoid) aside for future examination. (The 

 larynx is described at page 230.) 



Temporo-hyoideal Articulation. This joint will be found intact at 

 the base of the skull. It is a typical amphiarthrodial joint, the toe-like 

 extremity of the great corna being joined to the hyoid process of the 

 petrous temporal bone by a short rod of cartilage (about half an inch in 

 length). The interposed cartilage is sufficiently long and ilexible to 

 permit a considerable range of movement. By these joints the hyoid is 

 suspended to the base of the skull, and swings backwards and forwards 

 in movements comparable to flexion and extension. These movements 

 are concerned in the actions of mastication and deglutition. 



The Intercornual Articulation. This is another amphiarthrodial 

 joint, the opposed extremities of the great and the small cornu being 

 united by intermediate cartilage. In this cartilage there is frequently 

 to be found a small pea-like nucleus of bone which is the representative 

 of a third cornu — the epihyal of comparative anatomy. 



The Basi-cornual Articulation. The lower extremity of the small 

 cornu is articulated to the body of the hyoid in a small diarthrodial 

 joint provided with a capsular ligament and a synovial membrane. The 

 small cornu and the thyroid cornu form at this joint an angle, and the 

 movements are extension and flexion. 



Birections. — The dissector will now be able to trace the anterior root 

 of the occipital vein to its origin from the subsphenoidal sinus, and 

 thereafter the anterior and lateral straight muscles of the head are to 

 be dissected. 



The Subsphenoidal Sinus (or confluent). This is a venous sinus 

 placed at the inner edge of the foramen lacerum basis cranii. It extends 

 downwards (the head being vertical) for half an inch below the carotid 

 notch, the sphenoid bone being there depressed for the sinus. At this 

 extremity it terminates blindly. Traced upwards, it lies along the 

 inner edge of the foramen lacerum (the basilar process being depressed 

 beneath it), and it is directly continued as one of the roots of the 

 occipital vein. A little above its lower extremity the sinus is pene- 

 trated by the internal carotid. Slit open the sinus, and observe that 

 it communicates by an oval foramen with the cavernous sinus of the 

 dura mater. This oval foramen has its broad end circumscribed by the 

 carotid notch of the sphenoid, and for the remainder of its extent it 

 is bounded by the fibrous tissue that fills up the greater part of 

 the foramen lacerum. Through the forepart of this oval foramen the 

 carotid artery passes' from the subsphenoidal to the cavernous sinus, 



