62 



THE HUMAN BODY 



foramen magnum is an occipital condyle (Fig. 26, oc). These 

 are the points at which the skull rests upon the atlas. The orbits 



or eye. sockets are outlined in front 

 by the frontal, malars, and max- 

 illae. The space behind the orbit, 

 between the malar and temporal 

 bones, is occupied by a large mus- 

 cle which closes the jaw. The shape 

 of the face depends very largely 

 upon the malar bones. The an- 

 terior nares, or openings of the nos- 

 trils are bounded by the maxillae 

 and nasals. The posterior nares, by 

 which the nose communicates with 

 the throat cavity, lie behind the pal- 

 FIG. 26. The base of the skull, ate bones (Fig. 23). Enlargements 



The lower jaw has been removed. ,. ,, , . ,, 



At the lower part of the figure is of the temporal bones contain the 



the hard palate forming the roof of auditory a pp ara tus. 



the mouth and surrounded by the 

 upper set of teeth. Above this are 

 the paired openings of the posterior 



The Hyoid. Besides the cranial 



, and a short way above the and facial bones there is, as already 



pointed out, one other, the hyoid 



( Fi S' 27 )> which reall y belon g S to 

 the atlas, on its sides; V, the the skull, although it lies in the 



vonier; Pt, the palatines. , T , , ,. . ,, f 



neck. It can be felt in the front 



of the throat, just above "Adam's apple." The hyoid bone 

 is U-shaped, with its convexity turned ventrally, and consists 

 of a body and two pairs of processes called cornua. The smaller 

 cornua (Fig. 27, 3) are attached to the base of 

 the skull by long ligaments. The bone serves 

 as an attachment for the base of the tongue. 

 The hyoid is of much interest from the stand- 

 point of comparative anatomy because in the 

 very young Human Body it is a part of a struc- 

 ture which corresponds to the gill mechanism SI 

 of fish, tadpoles, and similar aquatic animals, consisting of several 

 gill arches with gill clefts between them. In the human embryo 

 the gill clefts close before birth, and all the gill arches disappear 

 except those which persist as 'the hyoid. It is difficult to explain 

 the development and subsequent disappearance of this structure 



FIG. 27. The hy- 

 oid bone. 1, body; 

 cornua; 3, 



