AND ITS APPENDAGES. 651 



becomes repeatedly subdivided, forming the bronchial tubes and 

 their ramifications. At first, the lungs project into the upper 

 part of the abdominal cavity ; for there is still no distinction be- 

 tween the chest and abdomen. Afterward, a horizontal partition 

 begins to form on each side, at the level of the base of the lungs, 

 which gradually closes together at a central point, so as to form 

 the diaphragm, and finally shuts off altogether the cavity of 

 the chest from that of the abdomen. Before the closure of the 

 diaphragm, thus formed, is complete, a circular opening exists on 

 each side the median line, by which the peritoneal and pleural 

 cavities communicate with each other. In some instances the de- 

 velopment of the diaphragm is arrested at this point, either on one 

 side or the other, and the opening accordingly remains permanent. 

 The abdominal organs then partially protrude into the cavity of 

 the chest on that side, forming congenital diaphragmatic hernia. 

 The lung on the affected side also usually remains in a state of 

 imperfect development. Diaphragmatic hernia of this character is 

 more frequently found upon the left side than upon the right. It 

 may sometimes continue until adult life without causing any seri- 

 ous inconvenience. 



The heart is formed, at a very early period, directly in front of 

 the situation of the oesophagus. Its size soon becomes very large 

 in proportion to the rest of the body ; so that it protrudes beyond 

 the level of the thoracic parietes, covered only by the pericardium. 

 Subsequently, the walls of the thorax, becoming more rapidly 

 developed, grow over it and inclose it. In certain instances, how- 

 ever, they fail to do so, and the heart then remains partially or 

 completely uncovered, in front of the chest, presenting the condition 

 known as ectopia cordis. This malformation is necessarily latal. 



Development of the Face. While the lower extremity of the 

 pharynx communicates with the cavity of the stomach, as above 

 described, its upper extremity also becomes perforated in a similar 

 manner, and establishes a communication with the exterior. This 

 perforation is at first wide and gaping. It afterward becomes 

 divided into the mouth and nasal passages ; and the different parts 

 of the face are formed round it in the following manner : 



From the sides of the cephalic mass five buds or processes shoot 

 out, and grow toward each other, so as to approach the centre of 

 the oral orifice above mentioned. (Fig. 243.) One of them grows 

 directly downward from the frontal region (i), and is called the 

 frontal or intermaxillary process, because it afterward contains in 



