64. Towards the end of the first month it is easy to distinguish the head of the fœtus, which has the appearance of a vesicle composed of thin membranes, and is as large as the rest of the body. The latter is straight—and there is in one part of the head a black dot, marking the spot for the eyes. (Plate I. fig. 5.)[12] But it is during the second month that the various parts of the face, as well as the superior and inferior extremities, become visibly delineated in the fœtus. The eyes are indicated by two black spots of considerable size, compared to the volume of the fœtus. The eyelids are not spread over them until the tenth week, at which time the external concha of the ear, as well as the profile form of the nose, become properly defined. At this same period we find the mouth, which was at first a simple opening of no mean size, becoming more distinctly delineated, owing to the formation of the lips. These soon approach each other, leaving a simple transversal slit or depression between them. (Plate II. fig. 11 and 12.)
65. The extremities appear in the form of globular tubercles at first; the superior preceding the inferior by a short period of time. Until between the third and fourth month, the lower are smaller than the superior extremities. Even at the latter month they are shorter than the projection of the os coccygis. The parts of reproduction may then be distinctly seen. In the male as well as in the female, these parts are exceedingly prominent. (Plate V. fig. 18 and 19.) But the difference of the sexes may be deduced from other circumstances besides the sexual organs. Such as the particular structure of the thorax and abdomen, the form of the head, the extremities, and the dorsal spine. (Autenrieth, Soemmering, Meckel, Velpeau.)
66. The external organs of the fœtus are all well defined at the end of the fourth month. The abdomen is fully covered in; the intestines are no longer visible. By the sixth month the fœtus is perfect in its shape and formation. In the seventh, eighth, and ninth months, its successive development is limited to mere size, volume, or amplitude, and a proportionate increase in weight. It is well to keep in mind, that although the growth of the various parts of the fœtus bears a proportion to the general development of its body, that part of the body which is above the navel, measures in length more than the part below it, until the full and complete period of gestation, when the navel marks the precise middle of the length of the fœtus. This circumstance assists us materially in forming our opinion respecting the age of any fœtus, either as a matter of curiosity, or as a guide in questions of forensic medicine. (Foderé, Chaussier.)