50 OSTEOLOGY. 



with this cavity, anteriorly, is an articular ridge, the condyle, 

 which also forms part of the articulation, and posteriorly the 

 anterior mastoid process, which limits the motion of the articu- 

 lation ; the opening of the parieto-temjjoral conduit or canal is 

 at the base of the process. Posteriorly, the bone divides, the 

 inferior portion being beaked, and clasping the external auditory 

 meatus of the petrosal bone, and the other extending backwards, 

 to articulate with the occipital, the occipital ridge becoming 

 continuous with the prolongation of the zygomatic spine. 



The internal surface is divided into two very unequal portions 

 by a deep channel, which forms, with the parietal and petrosal 

 bones, the temporal or parieto-temporal conduit. The posterior 

 portion articulates with the petrosal bone, while the posterior 

 half of the anterior and larger portion is greatly roughened and 

 bevelled, superiorly, forming with the parietal bone the squamous 

 suture of the skull : such of the remaining portion as forms part 

 of the wall of the cranial cavity is marked similarly to the internal 

 surface of the other cranial bones ; the remainder articulates 

 with the ali-sphenoid bone. 



Thus the squamosal bone articulates with the petrosal, parietal, 

 occipital, frontal, sphenoid, malar, superior and inferior maxillary 

 bones. 



The Petrosal bone is the hardest bone in the skeleton, and 

 is interesting, as it contains the essential part of the organ of 

 hearing. It is a small, thick bone, somewhat pyramidal in shape, 

 the base being turned downwards and a little backwards, and it 

 is placed at the postero-lateral part of the cranium between and 

 below the occipital, parietal, and squamosal bones. It presents 

 four surfaces, a summit, and a base. 



The anterior .surface is divided into two portions, the more 

 external part being roughened, and articulating by harmony with 

 the parietal bone, while the inner and lesser portion is smooth, 

 and forms the posterior part of the cavity for the greater lobe of 

 the cerebrum. The posterior surface is triangular and rough, 

 and articulates by harmony with the occipital bone. The external 

 surface, also triangular, is divided into two parts, the inner 

 articulating with the squamosal, the outer being interposed between 

 the occipital ridge and the styloid process of the occipital bone. 

 The internal surface, which forms the lateral boundary of the 

 cavity for the cerebellum, is slightly concave, and presents several 

 depressions, and anteriorly a large orifice and conduit, the internal 



