The lower border, much thinner, is tilted rather forwards to the right, by the passage of the superior mesenteric vessels beneath it, which separate it from the third portion of the duodenum ; on the left the inferior me senteric vein passes beneath it to join the splenic.
The anterior swface looks upwards as well as forwards, and is convex both transversely and longitudinally ; it is the only portion of the gland that is covered by peritoneum : from this circumstance, as well as from its being the free surface, it is very smooth.
The posterior surface contrasts strongly with the anterior, for being uncovered by peri toneum, and closely applied to all those struc tures ag,ainst which it lies, it presents many irregular elevations and depressions, corre sponding with the uneven surface which these structures contribute to form.
Size and weight. —The size and weight of the pancreas are liable to great variety, and hence different authors have stated them very variously. Wharton* gives its weight as five ounces; Meckel, from four to six ; Cruveilhier states its limit as six ounces, but thinks that a healthy pancreas may. be as small as two ounces and a half ; Scemmerring also considers six ounces a maximum, but carries his minimum as low as an ounce and a half. According to Krause and Glendinning, its usual weight is from two and a quarter to three and a half ounces. Its size is stated by Meckel as six inches long and one thick ; Ellis gives its length as seven inches ; Quain and Sharpey, from six to eight inches, with an average breadth of an inch and a half ; according to Wharton, its length is about five inches, its greatest breadth one and a half, and its thickness one inch. Of all these weights and measurements I think that of Wharton, which is the earliest, comes nearest the truth; only his measurement of leng,th is too little. From a large number of obser vations I find the average weight to be from four to five ounces, the length seven inches, the greatest breadth an inch and a half, and the thickness three quarters of an inch. It is smaller in womp than men, but only in proportion to the difference of size. Scemmerring saysl- that it is proportionately larger in the fcetus and the new-born infant than in the adult ; a statement that my own frequent observations have verified.
The specific gravity of this gland, accord ing to Muschenbroeck*, is, compared to water, as 2029 to 1000.
General appearance. — The best view of the external appearance of the pancreas is obtained on its anterior surface where it can be seen, through the peritoneum covering it, without any disarrangement of its structure. It is seen to be of a pale, clear, flesh colour, in which it strongly contrasts with the white cellular tissue investing it, with the yellow fat with which it is often surrounded, and with the grey and dingy coloured absorbent glands which lie contiguous. On looking more closely, it is seen to be mapped out into lobules, and this mapping out is sometimes more conspi cuously marked by the septa of areolar tissue that separate the lobules being loaded with fat. The lobules are of very various shapes and sizes, from an eighth to three quarters of an inch in diarneter, closely packed so as to fit into one another, and presenting an even general surface. But on a closer examination we see that these lobules are themselves sub divided by less conspicuous septa into a great number of smaller lobes ; and these again, especially if assisted by a little separation with a fine knife or needle, are seen to consist of numerous minute granules, or acini, as they are termed, which, as far as the scrutiny of the naked eye goes, appear to constitute the ultimate structure of the gland ; but, as we shall see more fully presently, the microscope shows these in their turn to consist of aggre gations of follicles, and therefore to he truly compound. Thus a mere inspection of the external surface of the pancreas gives an indication of its internal structure ; we see the acini by their aggregation constituting the lobules, the lobules the lobes, and the lobes the whole organ ; the association by which these parts are bound together being more and more intimate as we descend from the greater to the less ; but all of them, even the smallest, that come under the cognisance of the unassisted vision, being truly coinposite : this is a common character, and indeed a general description, of all conglomerate glands. The pancreas in consistence is inoderately firm, the lobules having a considerable degree of hardness, but the whole gland having a certain laxness about it, from the way in which the lobes are hung together by areolar tissue.