In all forms of abdominal hernia excepting those only which immediately supervene on penetrating wounds, the contents of the rupture are lodged within a pouch or bag termed the hernial sac, which is formed of the peritoneum. This membrane lines the entire cavity so per fectly and completely that nothing can pass out from it without the membrane also participating in the derangement and being pushed out before the displaced viscns. Once formed, this sac is rarely capable of being replaced or returned into the cavity of the abdomen ; never unless the hernia is small and recent, and " the cel lular substance accompanying it and the sper matic cord through the ring has not lost its natural elasticity and contractility." • Many surgeons have doubted the possibility of such an occurrence at any period,-1- but the fact has been demonstrated by dissection, and still more forcibly by the circumstance of the hernia having been thus strangulated within the ab domen when the sac has beeo returned along with it. as I have said, the sac when once formed is rarely capable of being replaced, nor does it long remain in this abnormal situation without undergoing some change in its patho logical condition—a change which it is not always easy satisfactorily to explain. In small bemire that have recently come down, the struc ture of the sac differs in nothing from that of the abdominal peritoneum ; and if the rupture is not reduced or kept up by a truss, it will pro bably increase in size without any remarkable alteration of tissue, for the membrane is ex tremely distensible, and will accommodate itself to any quantity of contents. But, if the hernia is easefully kept up, there can be no doubt that the sac will gradually contract and seem to rise up and approach the opening through which it originally passed, so that, although its cavity is never completely oblite rated, it is palpably diminished in size, and in capable of receiving and retaining the same quantity of contents it originally held. Some times in old and neglected herniae the sac seems to become so thin that the peristaltic motion of the intestines within it has been clearly perceived : this most frequently occurs in umbilical hernia, and is one of the reasons why this form of rupture was supposed not to have been enveloped in a sae at all. Again, on the contrary, in old licrniw also, and particularly where bandages have been worn to support or compress the tumour, it seems to become very thick, strong, and tense, and is said to have been met with as tough and as thick as cartilage. But in the great majority of instances these changes are rather apparent than real, and though doubtless the structure of the sac is no longer exactly that which it possessed before protrusion, the alteration is not so great as some writers have supposed. It was the opinion of Scarpa that an old hernial sac is in reality but slightly if at all thickened, and that the apparent thickening is caused by the con densation of the cellular tissue external to and around it. And here I may remark that diffe rences of opinion as to the altered structure of the sac may have arisen from a difference of accuracy and minuteness in examination, either during the progress of an operation or after death. NVe shall find hereafter that the normal anatomy of the parts connected with hernia is largely indebted to the knife of the anatomist for the shapes of the different openings, the division and enumeration of the different layers of fascia, and many other points; but in the morbid anatomy of the disease the same patient investigation and the same accuracy of descrip tion has not been so uniformly observed, and hence our knowledge of the latter part of the subject as compared with the former is by no means so defined and exact.
Where a rupture has been a long time down, it is not probable that the intestine shall thus remain in an abnormal situation without occa sionally suffering from inflammation, and hence adhesions between it and the sac are by no means unfrequently formed : the same effect may be produced by accidental violence, or from the latter cause the sac may be ruptured and its contents left lying under the usual coverings independent of the peritoneum. This is another of the cases in which a hernia has been supposed to exist without the invest ment of a sac.
The peritoneal aperture leading from the cavity of the abdomen into that of the rupture is narrow, and is called the neck of the sae : its dimensions as to length, however, vary with circumstances. As long as the communication is open and free between the two cavities, all that portion of peritoneum which is placed between them and corresponds to the canal through which the rupture has passed, may be termed the neck, and thus in inguinal hernia may be an inch, and in crural half an inch in length. But when the protruded parts are
strangulated, the little circle only around which the compression directly operates is more pro perly entitled to the appellation, and its extent is seldom greater than two lines. When the neck of the sac of a very recent hernia is viewed from the cavity of the abdomen, the peritoneum in its vicinity is seen thrown into slight folds or plaits, which appear to be prolonged downwards into the tumour; but on slitting open the neck, I have never seen this appearance within it, the membrane there being smooth, rather whiter and more opaque, and evidently thicker and more ur yielding than elsewhere. If such a hernia in the living subject has been reduced and kept up by a truss, the neck gradually contracts under the pressure, an its diameter with re spect to that of the ring through which it has passed is altered to a degree that is of the greatest importance in the event of another pro trusion, for it will be shown hereafter that such a diminution of size greatly predisposes to the occurrence of strangulation. It is also possible that the neck shall be so contraeted that in the new occurrence of hernia an additional portion of peritoneum may be detruded, and then the sac must present the shape of an hour-glass, narrow in the centre and broad at either end : sometimes two, three, or more of these succes sive protrusions take place, and then the sac is divided into so many sacculi with incomplete intercepts or partitions between them. Or one portion of peritoneum may be forced within another, so that the intestine is actually in cluded within a double sac. This last is a curious and very uncommon occurrence. On the other hand the neck of a hernial sac may suffer distension. In very old ruptures that have become irreducible or from any other cause been long down, the neck of the sac sometimes becomes wonderfully dilated, and the portion of intestine immediately passing through it scarcely subjected to the slightest pressure.
There is one form of hernia, the chief peculiarity of which lies in the nature of its peritoneal investment, for, correctly speaking, it possesses no proper sac. It is the hernia con genita,* a species of rupture which occurs in very young infants, and sometimes, under peculiar circumstances, in persons of a more advanced age also.
During the early periods of fatal existence the testes do not occupy that situation which they possess in after life. They are placed within the abdomen, above the pelvis, which at this time is so small and imperfectly developed that many of the viscera lodged within it after wards, seem now to lie within the belly. They are just below the kidneys, in front of the psoas muscle at each side, and possess, like other viscera, an investiture of peritoneum, which is afterwards to be- the tunica vaginalis testis. About the sixth month, or perhaps the seventh or even later, (for it observes no exact rule in this respect,) the testis begins to descend, not gliding behind theperitoneum,but preserving its own investing coat until it comes to the internal abdominal ring, where it pushes a process of peritoneum out before it, just as an intestine would do in the production of a hernial sac. This is afterwards to become the tunica vaginalis semi. The testicle then passes on through the inguinal canal, through the external ring,-1- and finally drops into the scrotum. After some time the canal of communication with the cavity of the abdomen begins to contract and close, and if the usual process goes on healthily and without interruption, very shortly a complete obliteration takes place, and the testis is sepa rated from the abdomen perfectly and for ever. The time at which this is accomplished is ex tremely uncertain : sometimes it is perfect at birth ; in other cases the canal is more or less open, and then, if the infant cries or struggles, a portion of the contents of the abdomen is protruded into the cavity of the tunica vaginalis, and the hernia congenita is formed. If any part of the above-mentioned process is interrupted or postponed, it will occasion some variety. Thus the tunica vaginalis may not exhibit its usual disposition to close and become obliter ated at its neck, and then for a length of time the patient is exposed to all the inconvenience and hazard of thedescent of a hernia: sometimes the testicle does not come down until a much later period, a circumstance that is often occa sioned by the gland contracting adhesions with some adjacent viscus in its passage, and may be attended with the additional inconvenience of drawing down such viscus along with it. The surgeon should also be aware of the possibility of the protrusion of another portion of perito neum into the open tunicavaginalis, and thus a mixed case may arise of a congenital containing within it a proper sacculatcd hernia.