U^ NORMAL HISTOLOGY. 



spleen, and growth from the blood-platelets, or hsematoblasts of 

 Hay em, have been advanced from time to time as additional sources 

 of origin of the red blood-corpuscles. Without entering upon a 

 detailed critical consideration of the evidence supporting these views, 

 it may be stated that, at present at least, they all lack the conclusive 

 proof of unimpeachable direct observation. Concerning the rela- 

 tions of the " haematoblasts" much confusion exists in consequence 

 of the application of the term to different objects by various writers. 

 The exceptionally small red corpuscles, or ' ' microcytes, ' ' together 

 with those of unusually large diameter, may be regarded as ex- 

 pressing the extremes of variation in size to which all morphological 

 elements are subject. The formative processes within the red bone- 

 marrow may be regarded, in the light of our present knowledge, as 

 the most important source, if, indeed, not the sole authentic one, of 

 the new red blood-corpuscles produced throughout life. 



Mention may be made in this place of the problematic organs the 

 so-called arterial glands, which include the coccygeal and carotid 

 glands. 



The first of these, the glandula coccygea, or Luschka's gland, 

 occurs near the tip, in front of the apex, of the coccyx, associated 

 with the middle sacral artery, which contributes the blood-vessels 

 largely forming its pea-sized mass. The carotid gland lies at the 

 bifurcation of the common carotid artery, frequently between the 

 resulting branches, and appears as a somewhat flattened ovoid 

 nodule. 



These peculiar bodies are identical in structure, both consisting 

 of dense arterial net-works surrounded by irregular groups of 

 granular polyhedral cells, whose presence suggested the once 

 supposed glandular nature of the organs. The entire plexiform mass 

 is invested by connective tissue, from which fibrous septa pene- 

 trate between the vascular structures. Numerous non-medullated 

 nerve-fibres are also present. 



The true nature and function of these rudimentary organs are en- 

 tirely unknown, and probably will remain so until the embryology of 

 these bodies is better understood. 



