824 GENERATION. 



closed in the formation of the face. The rest of this cavity remains closed 

 until a communication is effected with the oesophagus. The oesophagus 

 appears in the form of a tube, which finally opens into the pharynx above 

 and into the stomach below. At this time there is really no thoracic cavity, 

 the upper part of the stomach is very near the pharynx, the oesophagus is 

 short, the rudimentary lungs appear by its sides and the heart lies just in 

 front. As the thorax is developed, however, the oesophagus becomes longer, 

 the lungs increase in size, and finally the diaphragm shuts off its cavity from 

 the cavity of the abdomen. The growth of the diaphragm is from its pe- 

 riphery to the central portion, which latter gives passage to the vessels and 

 the oesophagus. When this closure is incomplete there is the malformation 

 known as congenital diaphragmatic hernia. 



The development of the anus is very simple. At first the intestine ter- 

 minates below in a blind extremity ; but at about the seventh week a longi- 

 tudinal slit appears below the external organs of generation, by which the 

 rectum opens. This is the anus. It is not very unusual to observe an arrest 

 in the development of this opening, the intestine terminating in a blind ex- 

 tremity, a short distance beneath the integument. This constitutes the mal- 

 formation known as imperforate anus, a deformity which usually can be 

 relieved, without much difficulty, by a surgical operation, if the distance be- 

 tween the rectum and the skin be not too great. The opening of the anus 

 appears about a week after the opening of the mouth, at or about the seventh 

 week. 



The rudiments of the liver appear very early, and, indeed, at the end of 

 the first month this organ has attained a large size. Two projections, or 

 buds, appear on either side of the intestine, which form the two principal 

 lobes of the liver. This organ is at first symmetrical, the two lobes being of 

 nearly the same size, with a median fissure. One of these prolongations 

 from the intestine becomes perforated and forms the excretory duct, of which 

 the gall-bladder, with its duct, is an appendage. During the early part of 

 foetal life the liver occupies the greatest part of the abdominal cavity. Its 

 weight, in proportion to the weight of the body at different ages, is as fol- 

 lows : At the end of the first month, 1 to 3 ; at term, 1 to 18 ; in the adult, 

 1 to 36 (Burdach). Its structure is very soft during the first months. As 

 development advances and as the relative size of the liver gradually dimin- 

 ishes, its tissue becomes more solid. 



The pancreas appears at the left side of the duodenum, by the formation 

 of two ducts leading from the intestine, which branch and develop glandu- 

 lar structure at their extremities. The spleen is developed, about the same 

 time, at the greater curvature of the stomach, and becomes distinct during 

 the second month. 



There is no reason to believe that any of the digestive fluids are secreted 

 during intrauterine life. At birth the intestine contains a peculiar sub- 

 stance, called meconium, which will be described farther on. Cholesterine, 

 an important constituent of the bile, is found in large quantity in the me- 

 conium. 



