in.] THE CRANIAL SKELETON. 87 



At birth the bone consists of two parts, which are separated 

 at the symphysis, and at first the ascending ramus slants 

 much backwards, but gradually rises till it is nearly vertical 

 in the adult. 



13. Another bone, often not reckoned as part of the skull, 

 is the os hyoides (so named from its resemblance to the 

 Greek letter v), which is placed beneath the root of the 

 tongue. 1 It consists of a " body " with a pair of processes 

 on each side, one large (the great cornu) and one small 

 (the lesser cornu, or corniculum). The body is transversely 

 oblong, hollowed behind, convex in front, and narrow from 

 before backwards. It is called the basi-hyal. 



The great cornua extend backwards from the lower outer 

 angle of this " body ;" they are rather long and nearly straight, 

 and though at first distinct bones, become anchylosed to the 

 basi-hyal. Each is also termed a thyro-hyal? 



The lesser cornua, or comicula t arise from the upper 

 aspect of the " body " at its junction with the greater cornua, 

 and each corniculum (or, as it is also called, cerato-hyalY is 

 attached to this " body " by a synovial sac, though sometimes 

 by bony union. Each corniculum is short and conical, and 

 united by a ligament to the styloid process of the temporal 

 bone. 



-==44: Considering now the OUTSIDE OF THE SKULL as a 

 whole, we find on its base in front the alveolar margin, 

 forming a graceful curve, and surrounding the bony palate 

 (with its palatine foramina), which extends a little further 

 back than the teeth, and ends in the posterior free margin 

 of the palatine bones. 



Behind the palate are the posterior nares, on each outer 

 side of which is a pterygoid fossa, bounded as before de- 

 scribed. In the middle of the basis cranii is the basilar part 

 of the occipital bone, behind it the foramen magnum, con- 

 dyles, and condyloid foramina. 



' On each side is the petrous part of the temporal bone, with 

 its styloid and vaginal processes and its carotid and stylo- 

 mastoid foramina. 



Between the front end of the petrous bone and the basi- 

 cccipital is, in the dry skull, an opening called the foramen 

 lacerum anterins. 



Between the hinder part of the petrous bone and the lateral 



1 For its more precise relations see Lesson XII. : the Larynx. 



2 From its being placed close to the thyroid cartilage of the larynx. 

 ' KfLiut', a horn. 



