THE SKELETAL SYSTEM 227 



The pituitary gland or hypophysis occupies a median depression of the 

 sphenoid, the sella turcica. A number of nerves and blood vessels have 

 their foramina of exit through the sphenoid, and a large foramen, the 

 foramen lacerum, marks its posterior boundary. 



The temporal bone is conspicuous on the sides of the skull, articulating 

 with the sphenoid in front, the parietal above, and the occipital behind. 

 Among its varied functions, it provides an articulation for the mandible 

 and a protection for the sensory ear. Its three divisions are the squamous, 

 mastoid, and petrosal. The squamous element covers the temporal 

 lobe of the brain and contains a fossa for the articulation of the mandible. 

 Several neck muscles, including the sterno-cleido-mastoid, are inserted on 

 the mastoid process of the temporal. The inner cavity or antrum of the 

 mastoid connects with the Eustachian tube and is consequently liable to 

 infection from the throat. Within the petrous portion of the temporal 

 are contained both the sensory and the bony portions of the inner ear. 

 The middle ear, lying between petrous and squamosal elements contain 

 the three ear bones, malleus, incus, and stapes, which belong to the 

 visceral skeleton. 



The ethmoid is a bone of delicate texture lying at the anterior end of 

 the brain case and articulating with the frontal, sphenoid, and other 

 bones. It consists of a dorsal, horizontal perforated plate, the cribriform 

 plate, a vertical mesethmoid plate which divides the nasal passages, and 

 paired lateral plates from which are derived the turbinal bones or conchae 

 of the nose. The inferior conchae, although fused with the maxilla in 

 the adult, are believed to be derived from the ethmoid. 



The vomer or "ploughshare" bone derives its name from its resem- 

 blance to a plough. It articulates with the mesethmoid and forms the 

 lower portion of the nasal septum. The lacrimal bones lie on the medial 

 surface of the orbit and are so named because the naso-lacrimal ducts pierce 

 them. They are the smallest bones of the cranium. The two nasal 

 bones form the bridge of the nose. They articulate with the frontal 

 above and the maxilla on the sides. 



The maxilla, in addition to its function as the upper jaw, helps also to 

 form the orbits, the palate, and the narial passage. As a part of the 

 visceral skeleton (splanchnocranium) its description will be taken up later. 



The posterior part of the hard palate is formed by the palatine, an 

 L-shaped bone, consisting of a vertical and a horizontal member, the 

 sphenopalatine notch dividing it into dorsal and ventral portions. It 

 articulates with sphenoid, maxilla, vomer, and ethmoid. 



The zygomatic or malar bones are quadrangular, with processes 

 articulating with the frontal, maxillary, and temporal bones. 



Development of the Cranium. The history of the vertebrate skull 

 revealed by the study of its comparative anatomy is amply supported 



