. Principles of human physiology : with their chief applications to pathology, hygiene, and forensic medicine : especially designed for the use of students. dFig. 74. Pancreas in Man bears considerable resemblance to that of the Mammary glands. In some of thelower tribes, however, they are much , in the Echinodermata and in Insects, theSalivary glands have the character of prolongedcceca, more or less convoluted; and the Pancreasof Fishes presents itself in the form of a cluster ofshort cceca round the pyloric extremity of thestomach, and opening into it by distinct ac
. Principles of human physiology : with their chief applications to pathology, hygiene, and forensic medicine : especially designed for the use of students. dFig. 74. Pancreas in Man bears considerable resemblance to that of the Mammary glands. In some of thelower tribes, however, they are much , in the Echinodermata and in Insects, theSalivary glands have the character of prolongedcceca, more or less convoluted; and the Pancreasof Fishes presents itself in the form of a cluster ofshort cceca round the pyloric extremity of thestomach, and opening into it by distinct accompanying figure will give a sufficientidea of the structure of these glands in Man; thecells are very minute, having a diameter onlyabout three times greater than that of the capillaryblood-vessels. Their development commencesLobule of Parotid gland of a from a simple canal, sending off bud-like pro- ZS£ SgyaSST1 cessf whi!* opens from the mouth, and liesamidst a vesicular blastema. As development pro-ceeds, the canal becomes more and more ramified, increasing at the expenseof the blastema, which is at last almost wholly absorbed; so that the sub-. LACHRYMAL GLAND. 533 stance of the gland consists of the ducts with their ramifications and cellularterminations, and of the blood-vessels which are distributed upon these. 694. The Salivary secretion is by no means necessarily constant, beingalmost or completely suspended by cessation of the movement of the masti-cator muscles and tongue, if unexcited by any nervous stimulus. Hence itis that the secretion is checked during sleep; so that, if the mouth be keptopen, its surface is almost dried up by the atmosphere. The mode inwhich the secretion is excited through the influence of the nervous systemhas already been considered (§§ 425,6). The quantity of saliva formed duringthe twenty-four hours, has been estimated at about 15 or 20 ounces; but onthis point it is evidently impossible to speak with certainty. The fluidobtained from
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