THE SKULL. 21 



drical at its cranial end. It is attached by its base to the 

 last segment of the body by a considerable cartilaginous in- 

 terval, while the opposite end is free and directed caudo- 

 ventrad. 



The cartilage of the ninth rib is attached to the lateral 

 face of the cartilage between the xiphoid and the body, and 

 just caudad of this the common cartilage of insertion of the 

 tenth, eleventh, and twelfth costal cartilages is attached, if 

 present. 



IV. THE SKULL. 



The bones of the head consist of the skull proper together 

 with' a number of separate bones forming part of the visceral 

 skeleton ; these are the lower jaw, the hyoid, and the ear- 

 bones. 



The skull proper is considered as divided into cranial and 

 facial portions. The former includes all the bones which take 

 part in bounding the cranial cavity or cavity of the brain ; the 

 latter includes the bones which support the face. 



The cranial portion of the skull includes all that part 

 enclosing the large cavity which contains the brain. For con- 

 venience this portion may be considered as made up of three 

 segments, each of which forms a ring surrounding a part of the 

 cranial cavity. The first or caudal segment or ring consists of 

 the occipital bone (with the interparietal) surrounding the 

 foramen magnum. The second segment consists of the 

 sphenoid ventrad, the parietals laterad and dorsad. Between 

 the first and second segments are intercalated laterally the 

 temporal bones containing the auditory organ. The third 

 segment or ring consists of the presphenoid ventrad, of the 

 frontals laterad and dorsad. The cranial opening of this ring 

 is closed by the lamina cribrosa of the ethmoid. 



The cranial portion of the skull therefore contains eleven 

 separate bones: one occipital, one interparietal, two temporals, 

 one sphenoid, two parietals, one presphenoid, two frontals, 

 and one ethmoid. 



The facial portion of the skull is much smaller than the 



