1400 



HUMAN ANATOMY. 



Basement 

 membrane 



Muscle-cell 

 Secreting-cells 



Parts of duct 



one-half or less of that of the ampulla, the duct loses the layer of muscle and 

 becomes flattened, with corresponding changes in the form of its lumen. The single 

 row of secreting elements is replaced by an irregular double or triple layer of 

 cuboidal cells, which exhibit an homogeneous zone, sometimes described as a 

 cuticle, next the lumen. On entering the epidermis, the duct not only loses its 

 fibrous sheath and membrana propria, but the epithelial constituents of its wall are 

 soon lost among the cells of the stratum germinativum, so that its lumen is continued 

 to the surface as a spiral cleft bounded only by the cornified cells of the cuticle. 



Apart from mere variations in size, certain glands — the circumanal, the ciliary 

 and the cer^iminous — depart sufificiently from the typical form of the coiled glands to 

 entitle them to brief notice. The circumanal glands, lodged chiefly within a 

 zone from 12-15 n^"^- wide and about the same distance from the anus, are not 



all the same, but include, 

 Fig. 1 1 65. according to Huber, four 



varieties. In addition to ( i ) 

 the usual sweat glands and 

 (2) some (Gay's) of excep- 

 tional size, (3) others have 

 relatively straight ducts that 

 end in expanded saccules, 

 from which secondary alveoli 

 arise ; finally (4) branched 

 glands of the tubo-alveolar 

 type are present. The cili- 

 ary glands (Moll's) of the 

 eyelid are not typical coiled 

 structures, but belong to 

 the branched tubo-alveolar 

 groups. The ceruminous 

 glands, distinguished by 

 the large amount of oil and 

 pigment mingled with their 

 secretion, are likewise refer- 

 able to the branched tubo- 

 alveolar type. 



The blood-vessels of 

 the sweat glands include 

 arterial twigs gi\-en of? from 

 the cutaneous rete, a capillary 

 net-work outside the mem- 

 brana propria, best developed 

 within the coiled portion of the tube, and the veins that join the deeper plexus 

 within the corium. 



The nerves are especially numerous and consist of nonmedullated sympathetic 

 fibres that traverse the fibrous sheath and form a close plexus on the outer surface 

 of the membrana propria. From this net-work fibrillje penetrate the basement 

 membrane and end in close apposition with the gland-cells and muscle-elements. 

 Their termination on the secreting cells is, according to Arnstein, in the form of 

 peculiar endings consisting of groups and clusters of minute terminal knobs with 

 which the nerve fibrillse, without or after division, are beset. 



THE DEVELOPMENT OF THE SKIN AND ITS APPENDAGES. 



The Skin.— The integument consists of two genetically distinct parts— the 

 epithelium (epidermis) developed from the ectoblast, and the coujiective tissue 

 (corium and tela subcutanea) from the mesoblast. During the earliest stages of 

 development the ectoblast is represented by a single layer of cells, which, by the end 

 of the first month, is in places reinforced by an external second layer, that by the 

 seventh week has appeared over the entire surface. This double layer now consists 



Parts of coiled 



secreting 



segment 



Muscle-cells 



Section of deeper coiled portion of sweat-gland. X 325- 



