THE BONES OF THE HEAD 123 



The small cornua are short conical nodules, each of which 

 projects upwards and backwards from the junction between the 

 body and great comu. Its tip gives attachment to the stylo- 

 hyoid ligament, which is sometimes ossified, a possible condition 

 to be borne in mind during digital examination of the upper part 

 of the pharynx. Elsewhere it gives attachment to the middle 

 constrictor muscle of the pharynx, and sometimes to the chondro- 

 glossus. The small cornua may be wholly or partially cartilaginous, 

 and they articulate with the body by a synovial joint, imles in 

 advanced hfe, when ankylosis usually takes place. 



Ossifieation. — The hyoid bone is developed in connection with the second 

 and third visceral arches. The cartilaginous bar of the second visceral arch 

 is known as the hyoid bar, and is continuous with its fellow at the median line. 

 The cartilaginous bar of the third visceral arch is known as the thyro-hyoid 

 bar, and at the median Une it blends with the junction of the hyoid bars. 

 With the foregoing proviso, the hyoid bone is developed from five, or. it may 

 be, six centres. One, or, it may be, two are deposited during the last month 

 of intra-uterine life at the place of fusion of the two hyoid bars. If there are 

 two centres they soon join, and give rise to the greater part of the body of the 

 hyoid bone or basi-hyaL About the same time a centre appears at either side 

 in the thjTO-hyoid bar of the third \-isceral arch, and from these centres are 

 developed the great cornua or thyro-hyals, and the adjacent portions of the 

 body. In the course of the first year the two remaining centres appear, one at 

 either side, in the lower or mesiad part of each hyoid bar, and these centres 

 give rise to the small cornua or eerato-hyals. The great cornua join the 

 body in middle life, but the small cornua do not join until advanced life. 

 The stylo-hyoid ligaments may become ossified more or less completely, and 

 50 represent the epi-hyal bones of many animals. 



The Skull as a Whole. 

 Sutures. 



The only bone of the skull which has movable articulations is the 

 mandible. Each condyle of that bone articulates with the anterior 

 part of the glenoid fossa of the corresponding temporal bone, with 

 the inter\'ention of an interarticular fibro-cartUage, the articulation 

 so formed being called the temporo-mandibular joint. 



The other bones of the skuU, for the most part, are in close con- 

 tact with each other, a small amount of fibrous tissue being inter- 

 posed, which is continuous with the periosteum. These articula- 

 tions are called sutures. Certain cranial bones, however, are separ- 

 ated at first by a plate of hyaline cartilage, the articulation being 

 called synchondrosis. This, however, is a temporary joint, inas- 

 much as ankylosis takes place after a certain period of Hfe. It 

 appHes to (i) the articulation between the basilar process of the 

 occipital and the body of the sphenoid, and (2) the articulation 

 between the jugvdar process of the occipital bone and the jugular 

 impression on the inferior surface of the petrous portion of the 

 temporal bone. 



The occipito-parietal or lambdoid suture connects the superior 

 lateral borders of the tabular part of the occipital bone with the 



