DEVELOPMENT OF THE TEMPORAL BONE. 



185 



Fig. 



205. 



Squamous portion 



Petro- 

 squamous 

 suture 



Incus 

 Stapes 



Petro- 

 mastoid 



Tympanic ring Malleus 



Tegmen tympani In 

 Inner wall Glaserian fissure 

 of tympanum 



Temporal bone at about birth, outer aspect. 



Fig. 206. 



Hiatus 

 Fallopii 



Petro-squamous suture 



spreads into the mastoid portion. This one is sometimes double. There is also a 



separate nucleus for the tegmen, but this is not constant. When present, it seems 



to be the last to fuse with the others, 



which become one by the end of the 



sixth month. The carotid artery passes 



at first along the base of the skull in a 



groove which is made into a canal by 



the opisthotic. The separated petrous 



portion, when ossification has made 



some progress, shows a very promi- 

 nent superior semicircular canal, and a 



deep cavity under it, extending back- 

 ward from the inner surface. This is 



the floccular fossa, which, however, is 



completely hidden by the dura. The 



mastoid process becomes fairly distinct 



in the course of the second year. It 



develops greatly about the time of 



puberty, when it becomes pneumatic. 



This may occur much earlier. J. J. 



Clarke has seen it wholly pneumatic several times before the tenth year ; once at 



three and a half.' The squamosal joins the petrous in the course of the first year. 



At birth the tympanic por- 

 tion consists solely of the im- 

 perfect ring open above. This 

 enlarges trumpet-like from the 

 edges, the front one forming 

 the tympanic plate. The 

 growth is of unequal rapidity, 

 so that the lower part is left 

 behind, presenting a deep 

 notch the outer edges of 

 which meet by the end of the 

 second year, leaving a foramen 

 below, which usually closes 

 two or three years later, but 

 exceptionally persists. The 

 tympanic plate fuses almost at 

 once with the petrous, but the 



Glaserian fissure remains ; the groove showing the line of union of the tympanic and 



mastoid processes generally disappears in the second year, but occasionally persists 



through life. Kircher^ found it present on 



both sides in five per cent, of 300 skulls. 



The styloid process consists of two parts. 



The first joins the petrous at about birth. 



The second, which represents all but the 



base, is an ossification of the stylo-hyoid 



ligament, and does not join till puberty 



or later. In very early foetal life the 



chief vein returning the blood from the 



brain passes through the membrane that 



is to become the squamosal. This open- 

 ing — the forai7ieyi jugulare spiirium — 



is later of less importance, and is finally 



closed. In the skull, at birth, a pin-hole 



representing it may be found at the postglenoid tubercle 



later. 



Position of superior 

 semicircular canal 



Posterior semicir- 

 cular canal 

 Floccular fossa 



Aquasductus 

 vestibuli 



Carotid canal 



Internal auditory canal 

 Temporal bone at about birth, from above and within. 



Fig. 207. 



Malleus 



External 

 auditory 

 meatus 



Tympanic ring 



Tegmen tympani in 

 Glaserian fissure 



Tympanic portion of temporal bone in the second year. 



It is sometimes seen 



' Journal of Anatomy and Physiolo,2:y, vol. xxvii., 1893. 

 ^ Archiv fiir Ohrenheilkunde, Bd. xiv., 1879. 



