462 MANUAL OF HISTOLOGY. 



(see 183). The following are the conclusions drawn from his investiga- 

 tions. In the first place, medullated nerve fibres make their way as far 

 as the gland vesicles, then pierce the membrana propria of the latter 

 (fig. 444, I.), and so get between the cells of the gland. The terminal 

 filaments, however, advance still further (II.), penetrating into the very 

 body of the cells, arid end in the nuclei of the latter (III.) 



The nerve fibres, further, are connected with multipolar cells declared 

 by Pfliiger to be ganglion corpuscles. These are situated on the external 

 aspect of the membrana propria (IV.), sending their processes from thence 

 into the protoplasm of the gland cells. 



Pfliiger describes, finally, another set of fibres which become resolved 

 into pencils of the most delicate primitive fibrillae, which become fused 

 eventually with the bodies of the epithelial cells lining the ducts. These 

 it is which produce that longitudinal striation beneath the nucleus already 

 spoken of. 



For the present we defer giving any opinion as to these statements, but 

 must just remark that we have never been able to find anything of the kind, 

 and have already described the ganglion corpuscles alone as connective- 

 tissue cells, entering into the structure of the walls of the gland vesicles. 



But little attention has, up to the present, been given to the texture of 

 the suMingual glands. From Heidenhain we learn that in the dog they 

 appear to be very similar in structure to the submaxillary, and to have 

 likewise two kinds of cellular contents, mucous elements surrounded by 

 border cells. The groups of the latter, however, are usually larger than 

 in the submaxillary gland, and in many instances extend around the 

 whole circumference of the gland vesicles. Sometimes even the latter are 

 entirely devoid of mucous cells. The interstitial connective-tissue of this 

 gland, farther, is remarkable for the great abundance of lymphoid cells 

 Avhich it contains. 



The ducts of Bartliolini and Rivin are completely destitute of muscular 

 fibres. 



Comparatively little is known also about the structure of the parotid 

 gland. In its wall we find the same flattened multipolar elements already 

 mentioned in speaking of the submaxillary organ. The diameter of the 

 gland-vesicles is 0'0338-0'0519 mm., and the granular cells contained in 

 them O'135-O'OISO mm. Mucous metamorphosis of the latter is never 

 met with, however, either in man or the lower animals. Their excretory 

 ducts are lined with ordinary epithelium, none of that fibrillation of the 

 lower half of the cells being seen here which is to be found in the sub- 

 maxillary gland. In the interior of the parotid, and several other race- 

 mose glands, possibly also in the submaxillary of many mammals, the 

 commencement of the excretory canals is formed of a different species of 

 cells, the so-called " centro acinal " cells first discovered by Langerhans 

 in the pancreas (see below). These are flat elements resembling vascular 

 epithelium usually of spindle or more rarely stellate figure. They bound 

 an axial canal of the acinus more or less perfectly. According to Pfliiger 

 the termination of the nerves is the same, as in the submaxillary gland of 

 the rabbit. 



The development of the salivary glands is on the same plan as the race- 

 mose. They commence to be formed in the human embryo in the latter 

 half of the second month. They are then seen as solid aggregations of 

 cells from which they are developed by gemmation. At the third month 

 they are already pretty well marked. 



