The lower border is bounded by the inferior horizontal portion of the duodenum, from which it is separated, near the middle line, by the superior mesenteric vein and artery, which notch it, and which also separate it from its reflected portion or head.
The right extremity is engaged in the duo denal fold in the manner described, and is in relation with the ductus choledochus. From the intimacy of its attachments to the duode num, it always accompanies this intestine in its displacements, so that when the duodenum is situated lower down than usual, which happens in displacements of the stomach downwards, the head of the pancreas is al ways removed in the same direction.
The left extremity is in relation with the left kidney, and with the spleen upon which it is sometimes flattened and blunted, and sometimes slightly enlarged, and to which it is attached by the intervention of the splenic veins, which send many branches into its sub stance : sometimes it does not extend quite so far as the spleen by half an inch or an inch.
Shape.—From its elongated form, the pan creas has been described by anatomists as possessing a body and two extremities; and of these extremities one, which is enlarged and clubbed, has been called the head; the other, tapering and acuminated, has been called the tail ; the middle portion, the great mass of the gland, being the body: other describers* have suppressed the body altogether, and de scribed as the tail all that portion which is not included in the curved intumescence at the right extremity, which they designate the head. Indeed the imaginations of anatomists have been largely drawn on to supply analogies whereby to illustrate the shape of this organ. Some have compared it to a hammer,—some to a dog's tongue; among them all I think the best is that which compares it to a pistol.
But, passing by these fanciful resemblances, the pancreas, from its transverse elongation and antero-posterior flattening, presents for description a right and left extremity-, an upper and lower border, and an anterior and posterior surface ; and these parts I shall de scribe in succession in the order in which I hale mentioned them.
The right extremity, to which the name head has been assigned, is that portion which is engaged in the duodenal curvature, and to which, from its occasional separation from the rest of the gland, the name of lesser pancreas has also been givenf : it differs from the rest of the gland in being thicker and more mas sive, curved instead of straight, and situated on a more posterior plane. It is thus formed :
—when the pancreas, in passing from left to right, has arrived at the duodenum, it be comes closely attached to that viscus, and follows its course, first downwards, and then to the left, passing by its extreinity, behind the superior mesenteric vessels, for which it thus forms a sort of groove or channel. It is by the fusion and massing of this curvature that the head is formed ; but in very young subjects, and in the lower animals, the curva ture of the pancreas is as conspicuous as that of the duodenum, and by separating it from its attachments, and straightening it out, all ap pearance of head vanishes, and it becomes a long prism, or flattened cy linder of even thick ness throughout.
In the human adult, however, it is impos sible thus to unravel and straighten the right extremity ; and the fusion of the parts has often proceeded to such an extent as entirely to obliterate the original curvature, the groove for the vena portm and superior mesenteric vessels being the only trace of its concavity.
The left extremity gradually tapers, getting both narrower and thinner ; it is sometimes bifurcated, sometimes blunted and flattened against the spleen, and sometimes slightly enlarged ; it presents nothing for special de scription.
The upper border is much thicker than the lower, so much so, that some anatomists have described the gland as being prismatic.
In the middle the cceliac axis rests upon it ; to the right the hepatic artery and first portion of the duodenum are in contact with it, and to the left it is deeply grooved by the splenic artery.
This groove does not run along the top of the border, parallel to it, but crosses it ob liquely from behind forwards as it passes to the left extremity, curving over it, as it were, so that while the commencement of the ar tery is behind the pancreas, its terniinal branches are in front (see fig. 54.). Some times this groove is converted into a canal, by the gland closing over it.