378 ORGAN SYSTEMS OF MAN 



the human face has been formed ( Fig. ventrally instead of posteriorly as is the case 

 X5-3). with most mammals. The large opening 

 The human skull is made up of 28 bones, through which it passes is called the fora- 

 22 of which are joined by jagged-edged men magnum. Since the skull is precari- 

 sutures (Fig. 13-30). The other 6 are the ously perched on the tip of the spinal col- 

 tiny ossicles of the ears. The bone which umn it might be expected that the cord could 

 supports the tongue and larynx, the hyoid, be broken at this point rather easily, and 

 is loosely connected with the skull. Although such is indeed the case. A severe blow at the 

 most of the skull is heavy, solid bone, cer- base of the neck will snap the cord at the 

 tain portions contain cavities. These are point where it enters the skull. This vulner- 

 remnants of chambers that formerly had able spot is taken advantage of by man in 

 specific functions but which apparently getting rid of his incorrigible fellows, by 

 have lost these and perform no known func- hanging. Other openings into the brain case 

 tion today. For example, the three sinuses in are the foramina for numerous small blood 

 the anterior and middle portion of the skull vessels and for the cranial nerves, including 

 once served the sense of smell but do not do the optic nerves at the base of the orbits, 

 so now. There is a pair of maxillary sinuses At birth, several bones from the brain 

 in the cheek region, a pair of frontal sinuses case have not come together ( sutured ) , so 

 over the eyes, and a single sphenoid sinus that five spaces are left without bony cover- 

 in the posterior part of the nasal cham- ing. These are called fontanelles (little 

 ber. They all have small ducts which drain fountains — so named because they rise and 

 into the nasal chambers but the arrange- fall with each heart beat). This lack of 

 ment is such that drainage is not good, es- suturing before birth plays a very impor- 

 pecially when the membranes are swollen tant function in the birth process, for the 

 with a cold. Under such conditions the head of the child undergoes severe squeez- 

 large surface area of the sinus membranes ing while passing through the birth canal 

 becomes infected, causing the so-called and needs to change its shape to fit the 

 sinus trouble which is often difficult to narrow passage. Were the skull hard, the 

 treat satisfactorily. Another spongy bone, difficult process of being born might be 

 the mastoid, lying behind the external ear even more difficult or impossible. The head 

 may also become infected via the eusta- of the newborn child is very plastic and 

 chian tube and the middle ear. Such an can be molded into almost any shape, 

 infection can reach the brain because the Flathead Indians took advantage of this 

 mastoid is separated from it only by very fact by placing a board on the head of the 

 thin bone. Surgery, in which a portion of newborn, thus causing the forehead to have 

 the bone is removed, is one of the methods a peculiar flat appearance in the adult. As 

 of clearing up such infections. the child grows, the fontanelles gradually 

 The brain is exposed to the outside wall close, leaving five jagged lines at the junc- 

 in only one place, and that is in the nasal tures. The age of a skull can be told by 

 chamber. The floor of the brain case, where the clearness of these lines. They are faint 

 the olfactory nerves leave the brain and or absent in old skulls, 

 pass down into the nasal chamber, is called Injuries to the skull have been common 

 the cribiform plate. It is a piece of bone throughout man's history. Early skulls often 

 perforated with many small openings show evidences not only of natural injuries 

 through which the nerves pass and through but also of apparent deliberate removal 

 which, unfortunately, nasal infections can of small portions. Such drillings (called 

 reach the brain. trephining) seemingly had some religious 

 The cord enters the human brain case significance, but the remarkable thing 



