S04 



DEYELOPMEXT OF THE UEO-GENITAL ORGANS. 



Although blood ceases at once to pass through the foramen ovale 

 from the moment of birth, or as soon as the left auricle becomes filled 

 with the blood returning from the lungs, and the pressure ^Yithin the 

 two auricles is equalised, yet the actual closure of the foramen is more 

 tardy than any of the other changes now referred to. It is gradually 

 effected by the union of the forepart of the valvular fold forming the 

 floor of the fossa ovalis with the margin of the annulus on the left 

 side ; but the crescentic margin is generally perceptible in the left 

 auricle as a free border beyond the place of union and not unfrequently 

 the union remains incomplete, so that a probe may be passed through 

 the reduced aperture. In many cases a wider aperture remains for 

 more or less of the first year of infancy, and in certain instances there 

 is such a failure of the union of the valve as to allow of the continued 

 passage of venous blood, especially when the circulation is disturbed by 

 over-exertion, from the right to the left auricle, as occurs in the mal- 

 formation attending the morbus coeruleus. 



DEVELOPMENT OE THE GENITAL AND TJRINAEY ORGANS. 

 The development of the permanent genital and urinary organs in 



Fig. 598. 



Fig. 598. — Enlarged View from before op the Left 

 Wolffian Body before the Establishment op the 

 DISTINCTION op Sex (from Farre after Kobelt). 



a, a, h, d, tubular structure of the WoliBan bodj ; 

 e, Wolffian duct ; /, its upper extremity ; <y, its termina- 

 tion in .r, the iiro-genital sinus ; h, the duct of Miiller ; 

 i', its upper still closed extremity ; I:, its lower eud ter- 

 minating in the uro-genital sinus ; I, the mass of 

 blastema for the reproductive organ, ovary or testicle. 



birds and mammals, is preceded by the 

 formation of a temporary glandular organ with 

 which the principal parts of both these sets 

 of organs are in their origin connected. These 

 bodies are named the Wolffian bodies, after 

 their discoverer, C. F. Wolff". From this close 

 association of these organs, it becomes neces- 

 sary to describe their development together. 



PRIMARY FORMATION OP THE URO-GENITAL SYSTEM. 



Wolifian bodies. — The Wolffian bodies occupy a considerable space 

 in the abdominal cavity of birds and mammals from an early period of 

 fcetal life, extending at first from the fifth or sixth protovertebral seg- 

 ments to near the caudal extremity, in the form of two reddish prominent 

 ridges, one on each side of the primitive intestine, and below the proto- 

 vertebral columns and primitive aortaa. They are thickest in the middle 

 of their length, and taper somewhat at their upper and lower extremities. 

 They consist, when fully formed, of short slightly convoluted tubes 

 running transversely, connected on the inner side with vascular glome- 

 ruli, very similar to the Malpighian corpuscles of the permanent 

 kidneys, and leading along the outer border into a tube named the 



