492 



GLAND. 



with Ruysch that the bloodvessels and the 

 secreting canals are continuous with each other, 

 is clearly shown ; in short, Rolando was the 

 first modern anatomist, who, following in the 

 footsteps of Malpighi, pointed out the manner 

 in which the inquiry ought to be prosecuted, 

 and thus laid the foundation of those laborious 

 and interesting researches for which science is 

 principally indebted to the German anatomists, 

 and by which, within the last few years, the 

 subject of the glandular organization has been 

 so strikingly elucidated.* 



Development. The investigations of Har- 

 vey, Malpighi, Rolando, Weber, Meckel, Bar, 

 Valentin, Rathke, Miiller, and many other 

 anatomists, have very satisfactorily determined 

 the manner in which the glands are in general 

 developed. It is, however, necessary to pre- 

 mise that these observations principally relate 

 to those glandular organs which are appended 

 to the alimentary canal, especially the salivary 

 glands, the pancreas, and liver ; for as regards 

 the development of those glands that are 

 subordinate to the secretion of urine and to 

 generation, comprising essentially the kidney 

 and the testis, much uncertainty still prevails, 

 although it is rather generally believed that the 

 corpora Wolffiana, or false kidneys, are in some 

 way or other connected with their primary for- 

 mation .f 



From the researches that have been made 

 with so much care, we learn that, although 

 there are many modifications of the formative 

 process in the different classes of the glandular 

 organs, there are yet certain fixed laws in 

 obedience to which they are produced. As the 

 development of the individual glands is, how- 

 ever, considered in the several articles on those 

 organs, it is only requisite to describe in this 

 place in a general manner, and without no- 

 ticing the modifications of the general rule, 

 the process of formation. In prosecuting this 

 inquiry two different objects present themselves 

 for examination, the primitive substance in 

 which the gland is developed, and the internal 

 component parts, consisting essentially of the 

 secreting tubuli and the bloodvessels. 



1 . Every gland is formed from a portion of 

 the primary plastic and amorphous mass 

 ( blastudermu) of which the body of the embryo 

 consists. 



2. This mass is at first gelatinous, extremely 

 delicate and diaphanous ; it subsequently be- 



* Journ. Comp. des Sc. Med. xvi, p. 54, p. 57. 

 P. 63. The honour of discovering the mode in 

 which the glands appended to the alimentary pas- 

 sage are formed by pushings-out of that tube has 

 been by Burdach improperly attributed to Rathke. 



t It would be inconsistent with the perfection 

 of the formative process to conceive that either the 

 kidney or the testis requires the aid of any other 

 glandular organ for their development ; besides 

 which it may be mentioned that there is no actual 

 connexion between the above glands and the corpora 

 Wolffiana. Rathke observes, " Although they 

 (corpora Wolffiana) are not organically connected 

 with the kidneys and genital organs, they appear 

 to be, in an early period of the life of the embryo, 

 the precursor or representative of the kidney." 

 Burrtach, II. Band. p. 646. 



comes thicker and less transparent. In the 

 beginning it is solid, and in the case of those 

 glands which are appended to the alimentary 

 canal, that is to say, the salivary glands, the 

 liver, and the pancreas, (and the same laws 

 are observed in the formation of the lungs,*) 

 it appears as a projection on the mucous mem- 

 brane. (Fig. 222, A.) 



Fig. 222. 

 A 



D 



A pltm designed to show tlie first origin of the glands. 



a, 6, alimentary canal ; g, gland. (The letters 

 have the same signification in A, B, C, D.) 



3. In a short time this rounded mass begins 

 to project on its external surface, and thus 

 forms a number of lobes, or, as it were, little 

 islands, which, by the continuation of the same 

 process, become more and more numerous and 

 smaller in size; and thus, according to the cha- 

 racter of the gland examined, are at length 

 formed all the minute lobes of which it con- 

 sists. (Fig. 122, B.) 



4. Simultaneously with this development of 

 the outer surface of the plastic mass, but quite 

 independently of it, a metamorphosis is going 

 on within, by which the internal canals, which 

 subsequently become the secreting tubes, are 

 formed. In the first instance a hollow or 

 cavity is noticed communicating with the tube 

 of the intestine, and which subsequently be- 

 comes the principal or excretory duct. When 

 it first appears it is a simple sac, (Jig. 222, C,) 

 but in proportion as the projections or lobes 

 are formed on the external surface, lateral 

 branches are added to the principal duct ; and 

 these again become more and more ramified, 

 till an indefinite number of tubes are formed. 

 (Fig. 222, D.) 



* Rathke, in Burdach's Phy. II. Band. p. 680, 

 edit. 1837. Valentin, 1. c. p. 501 ct eq. 



