*894 BIRTH. 



always remains as a pit or depression ; this is the olfactory or nasal pit, to which the olfactory 

 nerve afterwards semis its branches. For the formation of the nose, see p. 879. 



Organ of Hearing. On both sides of the after-brain or posterior brain vesicle, above the 

 first visceral or hyoid arch, there is a depression or pit formed in the epiblast, which gradually 

 xtends deeper towards the brain this is the labyrinth pit or auditory sac, which soon becomes 

 tl'ask .shaped (fig. 692, A, B). 



[The stalk, which originally connected the cavity of the sac with the surface, persists as the 

 aqueduct us vestibuli; and its blind swollen distal extremity as the saccus endolymphaticus, 

 or recessus vestibuli {Hculdon, fig. 692, r, v).] The pit is\iltimately completely cut off from 

 the epiblast, just like the lens, and is now called the vesicle of the labyrinth or primary 

 auditory vesicle. Its related portion forms the utricle, from which, at the 2nd month, the 

 semicircular canals and the cochlea are developed (fig. 692, D). The union with the brain 

 ocean later, along with the development of the auditory nerve. The first visceral cleft remains 

 as an irregular passage from the Eustachian tube to the external auditory meatus. The outer 

 iir appears at the 7th week. 



Organ of Taste. The gustatory papilla? are developed in the later period of intra-uterine life, 

 and several days before birth the taste-buds appear (Fr. Hermann). 



453. BIRTH. With the growth of the ovum, the uterus becomes more dis- 

 tended, its walls more muscular and more vascular, although the uterine walls are not 

 thicker at the end of pregnancy. Toward the end of gestation the cervical canal is 

 intact until labour begins, or at any rate it is but slightly opened up at its upper part. 

 After a period of 280 days of gestation, "labour" begins, whereby the contents of 

 the uterus are discharged. The labour pains occur rhythmically and periodically, 

 being separated from each other by intervals free from pain. Each pain begins 

 gradually, reaches a maximum, and then slowly declines. With each pain the heat 

 of the uterus increases ( 303), while the heart-beat of the foetus becomes slower and 

 feebler, which is due to stimulation of the vagus in the medulla oblongata ( 369, 

 3). 



[At the full time the membranes and placenta line the uterus. The membranes 

 consist, from within outwards, of amnion, chorion, decidua reflexa, and decidua 

 vera. The fundi of the uterine glands persist in the deep part of the decidua vera, 

 and thus form a spongy layer, the part above this being the compact layer in the 

 deep part of the placenta, <?.//., near the uterine wall, we have also the fundi of the 

 uterine gland persisting in the decidua serotina. When the placenta and mem- 

 branes are expelled after birth, the line of separation takes place in the part of 

 the membranes and placenta where the fundi of the glands persist. After labour 

 is completely finished, the uterus is lined by the remains of the spongy layer of the 

 decidua vera and serotina, e.g., is lined by a layer which contains the fundi of the 

 uterine glands. The new mucous membrane is regenerated by the growth of the 

 epithelium and connective-tissue in this part. The membranes expelled are made 

 up of amnion, chorion, decidua? reflexa?, and the compact layer of the decidua vera.] 

 The uterine movements during labour proceed in a peristaltic manner from the 

 Fallopian tube to the cervix, and occupy 20 to 30 seconds. In the curve registered 

 by these movements there is usually a more steep ascent than descent. 



[Power in Ordinary Labour. Sometimes the ovum is expelled whole, the membranes con- 

 taining the liquor amnii remaining unruptured. Poppel has pointed out that the force which 

 ruptures the bag of membranes is sufficient to complete delivery, so that, as Matthews Duncan 

 remarks, the strength of the membranes gives us a means of ascertaining the power of labour 

 in the easiest class of natural labours. Matthews Duncan, from experiments on the pressure 

 required to rupture the membranes, concludes that the great majority of labours are completed 

 by a propelling force not exceeding 40 lbs.] 



Polailfon estimates the pressure exerted by the uterus upon the foetus at each pain to be 154 

 kilos. [338'8 lbs.], so that, according to this calculation, the uterus at each pain performs 8820 

 kilogrammetres of work ( 301). [This estimate is certainly far too high.] 



After-Birth. After the fcetus is expelled, the placenta remains behind ; but it is soon 

 expelled by the contractions of the uterus. During the contraction of the uterus to expel the 

 placenta, a not inconsiderable amount of the placental blood is forced into the child ( 40). [It 

 is more probable that the child aspirates the blood from the fcetus portion of the placenta. 

 11ns can be seen in late ligature of the cord. The child may thus gain two ounces of blood.] 



