GENERATIVE SYSTEM. 289 



whose structure we have been investigating, are originally formed 

 in a situation remote from that in which they are destined to 

 carry on their functions: " the colt has no testicles," is the com- 

 mon observation of the uninformed on these matters ; and we 

 know ourselves that the purse is without them, but we know, in 

 addition, that they exist ready-formed within the abdomen, and 

 that they will descend at a certain period of age into their proper 

 receptacle, the scrotum. During the fcetal state, we find them 

 more or less developed, tinged with a blush of red, lodged under- 

 neath the psooe muscles, in contact with the inferior borders of 

 the kidneys, covered and retained in their situations by peri- 

 toneum, and concealed by the intestines around them. Here 

 they receive their arteries from the contiguous trunk — the pos- 

 terior aorta ; the vasa deferentia run forward to them ; and the 

 cremasters likewise turn forv\ard instead of backward: there 

 being at this time no such thing as a spermatic chord. Thus 

 placed, the testicle may be regarded as one of the glands of the 

 abdomen : indeed, it has considerable similarity to the kidney — 

 receiving its vessels from the same contiguous source, and send- 

 ing a long duct backward into the cavity of the pelvis : nor does 

 there appear any conclusive reason why it should not perform the 

 same office in that situation that it does in the scrotum, and par- 

 ticularly since it is known that in birds they remain within the 

 belly during life. From the part where the bloodvessels enter, 

 we find growing a whitish substance, extended backward, di- 

 minishing in breadth as it recedes, passing through the ring, 

 wJiere the fibres of the cremaster may be traced upon it, and 

 whence it is prolonged into the scrotum, growing nanower and 

 narrower until it vanishes : this substance, regarded by some 

 simply as a ligament, -was considered by Mr. Hunter as the 

 giibernaculum or pilot, by means of which the testicle is directed 

 in its passage from the abdomen into the scrotum. Quitting 

 the spot where it has been formed and matured, the testicle 

 gradually retrocedes, guided by the gubernaculutn, until it arrives 

 at the internal ring, which, at this time (like every other part of 

 the parietes) is closed by peritoneum : this temporary obstruction 

 it overcomes by drawing the membrane down along with it 

 through the ring, and carrying the pouch made thereby down 

 into the scrotum ; the gubernaculum at the time undergoing a 

 complete inversion. This accounts for the production of the 

 tunica vaginalis, and explains how that membrane comes to be 

 doubled or reflected : the testicle, receiving originally (as an ab- 

 dominal viscus) one close and adherent peritoneal tunic, and 

 acquiring another, which forms a loose covering, as it passes 

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