2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



bat, Other mammals and man, in the cranial bones of man, in the inner 

 wall of the 9th rib and in the infra- and supra-spinous fossae of the 

 scapula of man. The blood supply of the lower jaw and cranial bones 

 of the fish is derived from the dermal vessels which enter the bone 

 at various points and assume parallel positions in the bone substance, 

 while the blood supply of the long bones of the higher vertebrates 

 comes from two sources, viz. the periosteal vessels which send off 

 many small branches into the bone through entering canals (canals 

 of Volkmann and other canals), and the medullary arteries which 

 pass obliquely through the walls of the shafts into the medullary 

 canals where they divide into ascending and descending branches 

 from which small vessels are sent off into the walls of the bones and 

 here become continuous with the vessels from the periosteum. 



The blood supply of the flat bones, such as the cranial, is derived 

 from the vessels of the pericranial and endocranial membranes which 

 send off branches into the outer and inner tables of these bones com- 

 municating by way of the central medullary diploe. 



From a study of a large number of bone sections ^ there are found 

 to be three structural types and various type combinations ' which 

 enter into the formation of bone : these are the first, composed of 

 lamellae ; the second, composed of laminae ; and the third, composed 

 of Haversian systems. These three types are combined in various 

 proportions in the bones of different animals. The circulations 

 which are found to be present in the different types of bone also 

 present variations which are sufficiently distinctive in character to 

 form two circulatory types, viz., the branching, and the plexiform. 

 The branching type, composed of tree-like branches, is found in the 

 first type bones, the plexiform, composed of small, large and irregu- 

 larly shaped meshes enclosed by small vessels, is found in the second 

 and third type bones, while combinations of the branching and plexi- 

 form circulations are present in structural type combinations. 



In the demonstration of the circulations some difffculty arises in 

 the preparation of the bone slides. In small animals like the frogs 

 or other animals of the same size it is practically impossible since 

 the long bones are almost always round and tangential sections of 

 them are necessarily flat. In large animals the long bones have flat 

 areas of sufficient extent to make satisfactory sHdes. 



In the preparation of bone sections for the purpose of showing the 

 circulation, a flat surface of bone is selected and as large a piece as 



^ Number of sections of bones examined up to the present, 1000. 

 ^ A Contribution to the Comparative Histology of the Femur, by J. S. Foote, 

 M. D., Smithsonian Contr. to Know!., Vol. 35, No. 3, 1916. 



