DEVELOPMENT OF THE KIDXEYS. 



655 



CHAPTER XVI. 



Fig. 246. 



DEVELOPMENT OF THE KIDNEYS, WOLFFIAN 

 BODIES, AND INTERNAL ORGANS OF GENE- 

 RATION. 



THE first trace of a urinary apparatus in the embryo, consists of 

 two long, fusiform bodies, which make their appearance in the ab- 

 domen at a very early period, situated on each side the spinal 

 column. These are known by the name of the Wolffian bodies. 

 They are fully formed in the human subject, toward the end of the 

 first month (Coste), at which time they are the largest organs in the 

 cavity of the abdomen, extending from just below the heart, nearlv 

 to the posterior extremity of the body. In the foetal pig, when a 

 little over half an inch in length (Fig. 246), the Wolffian bodies are 

 rounded and kidney-shaped, and occupy a 

 very large part of the abdominal cavity. 

 Their importance may be estimated from the 

 fact that their weight at this time is equal to 

 a little over ^ of that of the entire body a 

 proportion which is seven or eight times as 

 large as that of the kidneys in the adult 

 condition. There are, indeed, at this period 

 only three organs perceptible in the abdo- 

 men, viz., the liver, which has begun to be 

 formed at the upper part of the abdominal 

 cavity ; the intestine, which is already some- 

 what convoluted, and occupies its central 

 portion ; and the Wolffian bodies, which pro- 

 ject on each side the spinal column. 



The Wolffian bodies, in their intimate 



structure, closely resemble the adult kidney. They consist of 

 secreting tubules, lined with epithelium, which run from the outer 

 toward the inner edge of the organ, terminating at their free ex- 



FCETAL Pro, % of an inch 

 long; from a specimen in the 

 author's possession. 1. Heart. 

 2. Anterior extremity. 3. Pos- 

 terior extremity. 4. Wolffian 

 boily. The abdominal walls 

 have been cut away, in on'.er 

 to show the position of the 

 Wolffian bodies 



