2l6 



HUMAN ANATOMY. 



— Great cornu 



itself can play freely on the flat glenoid. The socket gradually deepens, and as- 

 sumes something like its definite shape apparendy in the course of the third year. 



THE HYOID BONE. 

 This is a U-shaped bone ^ not in contact with any other, situated below the jaw 

 and above the larynx, with which its physiological relation is intimate. It gives 

 origin to a large part of the muscular fibres forming the tongue. It consists of a 

 central body, elongafed transversely, and of a pair of greater and lesser horns. The 

 convex anterior surface of the body looks forward and upward ; the posterior surface, 

 which is deeply hollowed, faces in the opposite direction. The front surface is divided 

 by a median and a transverse ridge into four spaces, of which the upper are the 

  larger. The greater cornua extend with a curve backward and a little upward. 



They are broadest at their front, and 

 Fig. 2.SO. as they pass backward are somewhat 



twisted, so that the upper surface 

 comes to look outward. Each ends in a 

 small knob. They are connected with 

 the body sometimes by fibro- cartilage, 

 occasionally by a synovial joint. The 

 lesser cornua, slender processes some 

 five millimetres long, are the bony ter- 

 minations of the stylo-hyoid ligaments. 

 There is usually a synovial joint be- 

 tween them and the body, which they 

 join at the ends of the upper border. 

 They may be connected by ligament, 

 and are not very rarely wanting, which 

 simply means that ossification has not 

 occurred at the lower ends of the 

 stylo-hyoid ligaments. The outline 

 of the body and greater horns is easily felt from the surface, and the whole bone 

 can be grasped and moved from side to side. 



Development. — As embryology shows, the basihyoid, or body, is connected 

 with the second visceral arch through the stylo-hyoid ligaments, the lower ends of 

 which become the lesser horns, or cerato-hyoids, and with the third arch by the 

 greater horns, the thyro-hyoids. The bone ossifies in cartilage, two nuclei appearing 

 (according to Sutton) in the fourth foetal month, one on each side of the median 

 line, and speedily fusing. A nucleus appears in each greater horn in the fifth month. 

 Statements as to the time of appearance of ossification in the lesser horns vary from 

 a few months after birth to the end of adolescence. The latter is probably nearer 

 the truth. The greater horns rarely coossify with the body before forty-five, but 

 after that age not infrequently. Indeed, in old age they are generally joined. The 

 lesser horns are rarely consolidated before advanced age. 



mall cornu 



The hvoid bone from in front. 



THE SKULL AS A WHOLE. 



In connection with the description of the skull as a whole, which is not intended 

 to recapitulate the points already mentioned, but to discuss the general features, 

 especially those resulting from the apposition of the distinct parts, let it be remem- 

 bered that the skull is an egg-shaped structure, and that the face is placed under its 

 anterior and middle fossae. 



The C'*anial Sutures. — There are three antero-posterior sutures, a median 

 and a lateral one on each side, and two transverse ones. The median antero- 

 posterior suture is the sagittal -^"^ it lies between the parietal bones, and is jagged, 

 except at the posterior part, which is usually straight. Occasionally the metopic 

 suture^ persists between the original halves of the frontal bone. It is rarely in direct 

 continuation with the sagittal. The coronal suture^ crosses the top of the head, sep- 

 arating the frontal from the parietals. It ends at the top of the great wing of the 



^ Os byoideum. - Sutura sagittalis. "^ S. frontalis. ^S. corooalis. 



