Observations on certain parts of the animal oeconomy : inclusive of several papers from the Philosophical transactions, etc. / by John Hunter ... ; with notes by Richard Owen.
- John Hunter
- Date:
- 1840
Licence: Public Domain Mark
Credit: Observations on certain parts of the animal oeconomy : inclusive of several papers from the Philosophical transactions, etc. / by John Hunter ... ; with notes by Richard Owen. Source: Wellcome Collection.
Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)
18/484
![the loins to the scrotum? It is evident that it cannot be the com- pressive force of respiration ; because the testis is commonly in tn scrotum before the child has breathed, that is, the effect has been pro- duced before the supposed cause has existed. Is the testis pulled down by the cremaster muscle 1 I can hardly suppose that it is ; because, if that was the case, I see no reason why it should not ta£e place in the hedgehog, as well as in other quadrupeds ; and it the musculus testis had this power it could not bring it lower than the ring of the muscle. Why do the testes take their blood-vessels from such distant trunks ? Those physiologists who have puzzled themselves about the solution of this question have not considered that in the first formation of the body the testes are situated not in the scrotum but immediately below the kidneys; and that therefore it was very natural that their blood-vessels should rise nearly in the same manner as those of the kidneys, but a little lower.* The great length of the spermatic vessels in the adult body will no doubt occasion a more languid circulation, which we may suppose was the intention of nature. The situation of the testis in the foetus may likewise account for the contrary directions of the epididymis and of the vas deferens in adult bodies, though these two in reality make only one excretory canal. In the foetus the epididymis begins at the upper end of the testis; and it is natural, considering it is an excretory tube, that it should run downwards. And it is as natural that the rest of the tube, which is called vas deferens, should turn inwards at the lower end of the testis, because that is its most direct course to the neck of the bladder. Thus we see that in the foetus the excre- tory duct is always passing downwards. But the testis is directed in its descent by the gubernaculum, which is firmly fixed to the lower parts of the testis and epididymis, and to the beginning of * [The singular course of the recurrent nerves results from a similar mechani- cal cause. At the period when the rudimentary larynx first derives its nerves from the par vagum, the head and trunk are not separated by a neck, the trachea is not formed, the heart is situated near the base of the cranium, and the branchial arteries given off from the bulb of the then single artery pass above the nerves in question. As the anterior extremities bud forth, the brachial plexuses are de- veloped and the neck begins to elongate; then the rings of the trachea are suc- cessively added, and the larynx, which before was close to the heart, is carried upward, and the recurrent nerves, restrained by their relations to the arteries, which are now converted into the subclavian on the right side, and aortic arch on the left, become proportionately elongated. The recurrent course of the branch Of the dental nerve which supplies the pulp of the incisor in the porcupine and the jaw the Gallery of the Hunterian Museum, No.*357 b. It is scarcely necessary to observe that the above mechanical explanation of the course of the recurrent nerves leaves the question of the final cause as open as before. Mr. Hunter, after giving the physical cause of the course of the spermatic artery, next proceeds to inquire into the intention of Nature with re- ference to that peculiarity.]](https://iiif.wellcomecollection.org/image/b21131545_0018.jp2/full/800%2C/0/default.jpg)
