OP THE DUCTLESS GLANDS: THE SPLEEN. 459 



of an inch. The contents of these vesicles are (1) a finely-granular plasma rich 

 in albumen, (2) nuclear corpuscles, usually from l-3000th to 1 -4000th of an inch 

 in diameter, (3) cells of from 1 -2000th to l-1350th of an inch in diameter, whose 

 membrane seems to be formed by a sort of precipitation of the granules upon the 

 nuclei, and (4) fatty particles of various sizes, the proportion of which varies. 

 Besides the fully-formed vesicles, the parenchyma also contains numerous iso- 

 lated cells, which have been thought to be vesicles in an earlier stage of deve- 

 lopment, but which would appear, from the observations of Mr. Gray ( 485), to 

 be rather cells as yet unclosed in vesicles. The Medullary substance, when 

 thin slices of it are examined, is found to be considerably more transparent than 

 the cortical ; this being due to the absence of fat-particles from its substance. 

 It does not contain any glandular vesicles; but consists entirely of a basis of 

 fibrous tissue, which is formed by processes that come off from the sheath of the 

 cortical substance, and which contains numerous bloodvessels and nerves. The 

 interspaces of this tissue, however, are occupied by a granular plasma, in which 

 are nuclei and cells in various stages of development. The cortical substance 

 has a much larger supply of blood than the medullary; for each of the gland- 

 vesicles is surrounded by a network, of arterial capillaries with long meshes, 

 derived from primitive branches of the supra-renal arteries ; whilst other branches 

 pass at once towards the medullary substance, and there break up into twigs, 

 which return by devious paths into the cortical mass, there to end in a capillary 

 network. This superiority in vascularity evidently has reference to the greater 

 functional activity of the cortical substance. The supra-renal capsules are by 

 no means copiously supplied with Lymphatics ; indeed, it is doubtful whether 

 these vessels penetrate their interior. The nerves of these organs (which are 

 all derived from the plexuses of the Sympathetic system) are particularly nume- 

 rous ; no such supply being possessed by any similar organs. 1 



485. The development of the Supra-Renal bodies also has been studied by Mr. 

 Gray (loc. cit.). He states that they arise on the 7th day of incubation as two 

 separate masses of blastema, situated between the upper end of the Wolffian 

 bodies and the sides of the aorta, being totally independent (as concerns their 

 development) of those bodies or of each other. At this period, their minute 

 structure bears a close resemblance to that of the spleen, consisting of the same 

 elements as that gland, excepting in the existence of more numerous dark gran- 

 ules, which give to the organ at a later period an opaque and darkly granular 

 texture. The gland-tissue of the organ, in the form of large vesicles, makes its 

 appearance on the 8th day ; and is evolved in the same manner as that of the 

 spleen, namely, by an aggregation of nuclei into circular masses, around which a 

 limitary membrane ultimately forms. These are at first uniformly grouped 

 together, without any subdivision into cortical and medullary portions ; but on 

 the 14th day, the first trace of this subdivision becomes manifest, by the aggre- 

 gation of the vesicles into masses which radiate from the circumference towards 

 .the centre of the gland; complete tubes being sometimes formed by the junction 

 of the vesicles, as indicated by the hemispherical bulgings on their walls. At 

 a later period, the organs increase in size, and attain their usual position ; 

 and a more complete subdivision into cortical and medullary portions is observed. 

 The earlier appearance of the vesicular structure of these bodies, as compared 

 with that of the Malpighian bodies of the spleen, is a fact of much interest, 

 when considered with reference to the period of greatest functional activity in 



1 It is a curious observation, which has been recently made by M. Brown-Sequard, that 

 injuries to the Spinal Cord in the dorsal region, occasion congestion and (after a time) 

 hypertrophy of the supra-renal capsules (" Gazette Medicale," Fevr. 1, 1852). It is no 

 objection to the idea that this change is dependent upon nervous agency, that no spinal 

 nerves proceed to these organs ; since we know that a large number of spinal fibres enter 

 the parts of the Sympathetic system whence they receive their supply. 



