THE FCETUS. 207 



superior, in which is to be observed, the summit behind, the bregma 

 and sinciput in front, the vertex in the middle, and which is bound- 

 ed below by the occipito-frontal circumference; another, inferior, 

 which is represented by the base of the cranium and posterior part 

 of the face; a third, anterior or facial, which is enclosed in the 

 fronto-mental circumference; the two last, lateral or temporal, 

 which comprise whatever is left out by the other, and whose dimen- 

 sions have reference, in labor, to those of the occipito-mental 

 diameter, which renders presentations of them highly disadvanta- 

 geous. 



532. The articulation of the head with the vertebral column 

 merits the most serious attention; for want of a careful study of it 

 a vast number of accoucheurs and midwives bring children still born 

 into the world, who, a few minutes before, were strong and full of 

 vigor. 



The union of the atlas with the occipital bone is a very close ar- 

 ticulation, which scarcely admits of any motion except flexion and 

 extension; that of the atlas with the axis is a rotatory ginglyraus, 

 so arranged, that if the pivot motion of the head is carried beyond 

 a quarter of a circle, the articular surfaces immediately separate 

 and the spinal marrow is at the same momeat compressed, torn, or, 

 even entirely broken off; so that, if the chin of the foetus turns so 

 far as to pass behind the point of the shoulder, death ensues im- 

 mediately. On the other hand, it is in the occipito-vertebral articu- 

 lation that we find the cause of the so frequent presentations of the 

 vertex rather than the face. In fact, when seen in an antero-poste- 

 rior direction, the head resting on the top of the spine represents 

 a lever of the third kind: during the efibrts of parturition, the power 

 being evidently represented by the vertebral column, the points of 

 rest and of resistance must necessarily be met with at the extremi- 

 ties of the occipito-mental diameter. Now, if the occiput almost 

 always descends first, while the chin descends but very rarely, it 

 depends upon the more advantageous action of the power upon the 

 occipital than upon the opposite extremity of this lever, the condyles 

 being nearer the former than the latter of these points. 



§. V. Of the Attitude, and Position of the Foe- 

 tus during Pregnancy. 



533. During the whole course of pregnancy the foetus is bent 

 forwards, so as to form a kind of circle, more or less complete; at 

 full term it is found with the head bent forwards, on the breast, the 

 feet turned up to the front part of the legs, the legs against the hind 

 part of the thighs, the thighs on the anterior surface of the abdo- 



