562 



ANATOMY OF VERTEBRATES. 



375 



Skull of child at Ijirtli 



epiphysis : they are joined by ligament to the thyroid cartilage ; on 

 which account, although homologous mth a pair of the ' cerato- 

 branchials' of fishes and batrachians, they are termed ' thyro-hyals.' 

 The Human skull presents varieties related to sex, age, and 

 race. Those of sex are exemplified in the smaller size of the female 

 skull, the more delicate proportions of the facial bones, the minor 

 prominence of the malars, mentum, and angles of the jaw. 



In the skull of the child at birth, fig. 375, the jaws, through the 

 non-developement of the teeth and their sockets, are relatively 

 smaller than in the adult ; but the facial angle, owing to the rapid 

 growth of the brain, is, perhaps, nearer to the Greek ideal, at the 

 period when the deciduous teeth are in 

 place: both the cerebral cavity and the 

 orbits are then relatively greater. The bones 

 of the face are shorter vertically, through 

 the non-developement of the ethmoidal and 

 maxillary sinuses ; the regular convexity of 

 the forehead is not broken by the promi- 

 nences of the frontal sinuses. The sutures 

 of the cranium are more linear, less den- 

 tated, and more numerous, through the 

 non-coalescence of the elements of the adult cranial bones. The 

 angle is more open between the ascending and horizontal ramus 

 of the mandible : the mentum is vertical or recedes. 



In the adult, fig. 371, the vertical extent of the jaws is in- 

 creased by the growth of the teeth and their sockets, while the 

 whole face is expanded by the developement of the maxillary 



sinuses and olfactory csLxity, 

 through the full growth of 

 the nasal and turbinal bones 

 and of the ethmoidal sinuses. 

 The palatine arch has ex- 

 tended backward, and the 

 posterior nares have become 

 more vertical. The ascend- 

 ing mandibular ramus forms 

 almost a rio-ht angle with 

 the horizontal one or ' body ' 

 of the bone. 



In extreme age, fig. 376, the teeth are lost, the alveoli become 

 absorbed, and the jaws are reduced in vertical extent to infantile 

 proportions. The mandibular angle again becomes more open ; 

 but the chin projects and is brought nearer to the nose when the 



Skull of aged Individual 



