THE CLAVICLE. 197 



The ramus is proportionately wide, and forms with the body an angle which is 

 very obtuse. 



The coronoid process rises considerably above the level of the capitulum, and 

 comes into close relationship with the crista infratemporalis. 



The capiturum, which is proportionately more expanded than in the adult, 

 occupies the somewhat laterally -directed shallow mandibular fossa of the temporal 

 bone. 



On viewing the lateral aspect of the skull, the meatus acusticus externus, as 

 such, is not seen ; it is replaced by the slender annulus tympanicus, which supports 

 the tympanic membrane. This ring of bone, incomplete above, is united by its 

 extremities superiorly to the inferior surface and lateral aspect of the squamo- 

 zygomatic part of the temporal bone. The ring itself is disposed so that it slopes 

 downwards, forwards, and medially ; as yet it fails to enter into the formation of 

 the posterior wall of the fossa mandibularis, and only at a later stage does it grow 

 laterally to form the floor of the external acoustic meatus. Through the ring 

 the labyrinthic wall of the cavum tympani is seen ; exposed on this surface are 

 the promontory, the fenestra vestibuli, and the fenestra cochleae. 



Posterior to the tympanic ring the sutura squamosomastoidea, still open, is seen 

 separating the pars mastoidea from the squama temporalis of the temporal bone. 

 On turning the skull over so that its inferior surface is exposed, the partes laterales 

 of the occipital bone are seen separated in front from the pars basilaris by a 

 suture, which runs through the occipital condyle on either side. Posteriorly an 

 open suture, which curves backward and laterally on each side of the posterior 

 margin of the foramen ovale, separates them from that part of the squama 

 occipitalis which is developed in cartilage. The squama occipitalis at this stage 

 exhibits a lateral cleft on each side, passing backwards from the fonticulus 

 mastoideus, which serves to indicate the line of union of the parts which are 

 developed in cartilage and membrane respectively. The latter, the superior, 

 sometimes separate, constitutes the os interparietale. 



DIFFERENCES DUE TO AGE. 



At birth the face is proportionately small as compared with the cranium, constituting 

 about one-eighth of the bulk of the latter. In the adult the face equals at least half the 

 cranium. About the age of puberty the development and expansion of some of the air- 

 sinuses, more particularly the frontal sinus, lead to characteristic differences in form in 

 both the head and face. 



The eruption of the teeth in early life and adolescence enables us to determine the 

 age with fair accuracy. After the completion of the permanent dentition, the wear of the 

 teeth may assist us in hazarding an approximate estimate. The condition of the sutures, 

 too, may guide us, synostosis of the coronal and sagittal sutures not as a rule taking place 

 till late in life. Complete obliteration of the synchondrosis between the occipital bone 

 and sphenoid may be regarded as an indication of maturity. In old age the skull 

 usually becomes lighter and the cranial bones thinner. The alveolar borders of the 

 maxillae and mandibles become absorbed owing to the loss of the teeth. This gives 

 rise to a flattening of the vault of the hard palate and an alteration in the form of the 

 mandible, whereby the mandibular angle becomes more obtuse. 



THE BONES OF THE SUPERIOR EXTREMITY. 



Clavicula. 



The clavicle, or collar bone, one of the elements in the formation of the 

 shoulder girdle, consists of a curved shaft, the extremities of which are enlarged. 

 The medial end, since it articulates with the sternum, is called the sternal 

 extremity ; the lateral extremity, from its union with the acromion of the scapula, 

 is known as the acromial end. 



The extremitas sternalis (sternal end) is enlarged, and rests upon the disc 



