41.  Which germ layer is tooth enamel derived from?  
A.  ectoderm
B.  mesoderm
C.  endoderm

42.  Which germ layer is the cardiovascular system derived from?  
A.  ectoderm
B.  mesoderm
C.  endoderm

43.  Which germ layer is the urinary bladder derived from?  
A.  ectoderm
B.  mesoderm
C.  endoderm

44.  Which germ layer is the brain and spinal cord derived from?  
A.  ectoderm
B.  mesoderm
C.  endoderm

45.  Which germ layer are the bones (except facial) derived from?  
A.  ectoderm
B.  mesoderm
C.  endoderm

46.  Which germ layer are the tonsils derived from?  
A.  ectoderm
B.  mesoderm
C.  endoderm

47.  Arrange the following in the sequence in which they form in the embryo.
(1) neural plate
(2) neural tube
(3) notochord
(4) primitive streak  
A.  1, 2, 3, 4
B.  1, 3, 2, 4
C.  4, 3, 1, 2
D.  4, 1, 3, 2
E.  3, 4, 1, 2

48.  The embryo is most sensitive to outside influences that can cause malformations during the  
A.  first two weeks after fertilization.
B.  third to the ninth weeks of development.
C.  ninth to the sixteenth weeks of development.
D.  twelfth to the twentieth weeks of development.
E.  twenty-first to twenty-sixth week of development.

49.  Which of the following is NOT a possible route for neural crest cells?  
A.  melanocytes
B.  autonomic ganglion neurons
C.  adrenal cortex
D.  sensory ganglia
E.  enteric nervous system neurons

50.  Cells of the neuroectoderm become all of the following EXCEPT the  
A.  brain
B.  spinal cord
C.  postganglionic autonomic neurons
D.  posterior pituitary gland