90 



PANCREAS. 



gland substance, and is continuous with that 

 which pervades the whole gland : it differs 

 not, therefore, from that which has been 

 already described. 



Fig. 62. 



Tesselated appearance of columnar epithelium lining 

 the pancreatic duct. (Magnified 200 diameters.) 



The epithelium is columnar, arranged ap- 

 parently in a single stratum, and presenting 

 a beautiful honeycomb appearance of closely- 

 packed hexagons and pentagons, when looked 

 at on its free surface. Further up, however, 

 near the extremities of the ultimate ducts, 

 the epithelium changes its character, and 

 becomes more globular, as is shown in Jig. 63, 

 which represents a portion of the epithelial 

 lining of a duct, about ^-^ of an inch dia- 

 meter, from the human subject. A certain ap- 

 proximation is here seen to the form of se- 

 creting epithelium, with which, however, it 

 strongly contrasts in its clearness and free- 

 dom from granular contents. 



Fig. 63. 



Portion of epithelium lining a small duct ^th of an 

 inch in diameter. From a Rabbit. (Magnified 300 

 diameters.) 



There is every probability of the existence 

 of a basement membrane here as in other 

 sub-epithelial situations, and it is probably 

 continuous with that which alone constitutes 



the walls of the ultimate ducts : for the fibrous 

 and muscular elements gradually diminish as 

 the ducts get finer, until in the smallest that 

 are seen all fibrous appearance has vanished, 

 and a homogeneous membrane alone remains. 

 According to Henle the homogeneous wall of 

 the smallest ducts consists of fibres fused and 

 run together in a plane ; a supposition that 

 would imply the non-existence of this mem- 

 brane in the larger ducts, where they are not 

 so fused. 



Capillaries. The arrangement of the ca- 

 pillaries remarkably resembles that of fat. 

 They form a close and pretty even-meshed 

 net work, open on all sides, among the meshes 

 of which the follicles lie, just as the vesicles 

 do in the case of fat ; so that the closeness 

 of the plexus is a measure of the size of the 

 follicles. Their general appearance is well 

 seen in the accompanying figure (Jig. 6-t.). 



Fig. 64. 



Arrangement of the capillaries of the pancreas. Frnm 

 a minute lobule of the pancreas of a young Rabbit. 

 (Magnified 80 diameters.) 



III. COMPARATIVE ANATOMY. 



Invertebrata, Certain organs connected 

 with the alimentary canal have in some of the 

 higher invertebrata received the name of pan- 

 creas ; but they have done so rather from their 

 position and interred function than from any 

 certain evidence of their use, or from their 

 anatomical structure. In Gasteropoda we find 

 the first indications of the organ, and it 

 presents in them the form of a single, long, 

 blind, glandular sac, communicating with the ' 

 beginning of the intestine ; such a pancreas 

 may be seen in the different species of Aplysia 

 and Doris, Tritonia and Scyllasa. 



Cephalopoda. The Tetrabranchiate Cepha- 

 lopods possess, attached to the upper part of 

 the intestine, a laminated sac, which receives 

 the canal into which the two main hepatic 

 ducts unite, and which diverts the bile by a 

 peculiar development of one of its laminae, 

 from flowing into the gizzard. Professor 

 Owen considers that the follicular structure 

 of this and the other folds of membrane 

 sufficiently indicate its glandular character, 



