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 
