FLOW OF BLOOD THROUGH BONES AND JOINTS 



165 



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row as an entirely closed vascular system; and c) 

 Bunting (18) pictured vessels lined with epithelium, 

 but with openings at various points communicating 

 directly with the medullary parenchyma. A survey of 

 the literature indicates no general agreement among 

 those who have studied the subject. 



I 'a librae 



In the lumbar and thoracic regions the aorta gives 

 off paired segmental arteries. These penetrate the 

 anterior groups of spinal muscles and continue pos- 

 teriorly in the horizontal plane to pass on either side 

 of the vertebral body and lie in direct contact with 

 the anterior and lateral wall of this structure (fig. 4) 

 to which small branches are contributed (56). Each 

 artery gives off a large branch in the trough formed 

 by the vertebral body and the transverse process. 

 This branch traverses the intervertebral foramen and 

 divides into three terminal arterioles (113). One of 

 these passes to the posterior surfaces of the two adja- 

 cent vertebral bodies. A second runs to the spinal 

 cord and its meninges. The third supplies the pos- 

 terior vertebral processes and surrounding soft 

 structures. 



The first branch mentioned above divides within 

 the spinal canal, one terminus running upward and 

 medially across the posterior surface of the vertebral 

 body under the posterior spinal ligament, to enter a 

 foramen about the center of the body. The other 

 terminus runs downward and medially to a similar 

 entrance in the center of the body of the next distal 

 vertebra. Thus, there are four diagonal arteries, two 

 from each side converging to enter the center of the 

 posterior surface of each vertebra, either through a 

 common foramen or through separate foramina. The 

 arterioles may coalesce or remain separate before 

 radiating to all parts of the centrum (113). The main 

 dorsal vertebral artery and the right and left antero- 

 lateral arteries appear to end in the middle of the 

 developing osseous spongiosa. No arterial branches 

 can be demonstrated beyond the center of the verte- 

 bral body. Irregular vascular canals can be seen in 

 the spongiosa and a diffuse network of thin-walled 

 channels is present in the surrounding cartilaginous 

 zone. Very small vessels perforate the cartilaginous 

 plate and tiny capillary channels permeate the can- 

 nulus fibrosa. The branches to the cord anastomose 

 freely with the anterior and posterior spinal arteries 

 which lie on the respective surfaces of the cord ex- 

 tending from within the skull to the end of the cord. 

 The pedicles, transverse processes, articular facets, 



and lamina have a good arterial blood supply through 

 the anastomosing branches of the posterior rami from 

 the paired segmental arteries (46). Similar anatomical 

 arrangements are true for the cervical vertebrae (56). 



The intervertebral disc tissues appear to offer an 

 important focus for degeneration as they are always 

 farthest from the arterial supply (46). 



Each lumbar vertebral body is drained by four 

 main venous trunks. Two leave the body, one on 

 either side from an anterolateral position at a level 

 just above the midline; two emerge as paired vessels 

 from the bony foramen in the center of the posterior 

 vertebral wall (110). The two posterior veins empty 

 at once into the anterior longitudinal meningo- 

 rhachidian veins of the posterior external plexus. 

 Direct connection with the corresponding lumbar 

 veins is made through the spinal rami of the latter. 

 The two anterolateral veins from the vertebral body 

 empty directly into the lumbar veins. The lumbar 

 veins passing horizontally are in direct communica- 

 tion with three great longitudinal or vertical venous 

 systems: a) posteriorly with the posterior external 

 venous plexus which extends vertically within the 

 spinal canal, external to the spinal cord membranes; 

 b) with the azygos or hemiazygos systems, and c) with 

 the inferior vena cava. 



Within the vertebral body the two posterior and 

 the two anterolateral veins meet to form a large 

 reservoir. Although these veins have the usual venous 

 structure beyond the vertebral periosteum, the wall 

 structure is replaced by a limiting membrane of 

 flattened endothelial cells within the body. Radiating 

 peripherally from the central venous basin are many 

 irregular columnar spaces which occupy approxi- 

 mately forty per cent of the entire vertebral body. 

 The more peripheral parts of the venous spaces con- 

 tain within their lumens a very large proportion of 

 hematopoietic tissue, together with reticuloendo- 

 thelial elements. Hematopoietic tissue is occasionally 

 found within the lumen of the central venous space 

 (no). 



Flat Bones 



The mandible appears to be the flat bone concern- 

 ing which the most information is available. The 

 periosteum and outer circumferential portions of the 

 osseous mandible are supplied by such adjacent 

 arteries as the facial, submental, inferior alveolar, 

 mylohyoid, mental, masseric, lateral pterygoid, medial 

 pterygoid, temporal and sublingual branch of the 

 lingual (36). One or more nutrient foramina passing 



