1536 



HUMAN ANATOMY. 



as in the case of the Hver, a distinct basement membrane is sometimes wanting, a 

 delicate suoporting- reticulum alone intervening between the blood-stream and the 

 protoplasm of the cells. Although subject to local deviations, conspicuously excep- 

 tional in the liver, the veins follow in general the course of the arterial branches, the 

 larger blood-vessels, together with the main excretory ducts, the lymphatics, and the 

 nerves, occupying the principal extension of the connective tissue into the glandular 

 mass. 



The lymphatics are represented by the larger trunks which follow the excretory 

 ducts and freely anastomose within the interlobular areolar tissue. After the intra- 

 lobular portion of the vessel is reached, its definite character is gradually lost until the 

 lymphatic channels are to be recognized only as the clefts between the bundles of 

 connective tissue separating the alveoli. 



Injected gastric mucous mem- 

 brane, showing capillary net-work 

 surrounding tubular glands. X 55- 



Section of submaxillary gland of rabbit ; upper 

 half of figure shows distribution of nerve-fibres 

 to alveoli ; lower half shows terminal ducts and 

 secretion-capillaries. X 290. (Retzius.) 



The nerves supplying the larger glands include fibres from two sources, the 

 cranial or spinal nerves and the sympathetic. They follow the interlobular excretory 

 ducts, around which plexuses are formed, ganglion-cells being frequent at the points 

 of junction. The stronger twigs contain a preponderating proportion of thick 

 medullated fibres, which become progressively less in size and number in their course 

 towards the alveoli. Upon reaching the latter the nerves consist almost entirely of 

 nonmedullated fibres, and in the end-plexuses around the alveoli such fibres alone 

 are present. The terminal distribution, as demonstrated by the Golgi and methylene- 

 blue methods, includes epilemmar and hypolemmar fibrillce, the former lying upon 

 and the latter beneath the basement membrane. The hypolemmar fibrillae pass into 

 the acini from the extra alveolar plexus formed by the filaments surrounding the base- 

 ment membrane. The ultimate relation between the terminal fibrillae and the glandu- 

 lar epithelium is still uncertain, but it may be regarded as established that the nerves 

 extend between and around the cells ; an intracellular termination, on the contrary, 

 is doubtful. Retzius, Ebner, and others agree in picturing the delicate perialveolar 

 plexus as consisting of tortuous and convoluted filaments which end in occasional 



