NO. lO THE CIRCULATORY SYSTEM IN BONE FOOTE 3 



possible is sawed out, tangential to the diameter of the bone, and 

 ground down to a suitable thinness which is determined by the ap- 

 pearance of the circulation. 



It is not the thinnest possible section, measured in microiis, that 

 is most desirable, but one of sufficient clearness to show the circula- 

 tion. During the grinding process it is necessary to examine the 

 section at short intervals in order to ascertain just when to terminate 

 the process. 



The following sections taken from the bone of fish, amphibian, 

 reptile, bird, mammal, and man have been studied, described, and 

 drawn for the purpose of showing the structure and the circulation 

 which belongs to it. 



CROSS AND TANGENTIAL SECTIONS OF THE LOWER JAW AND 



TANGENTIAL SECTION OF THE CRANIAL BONE OF THE MAS- 



CALONGE, ESOX, A FISH OF WISCONSIN WATERS 



CROSS SECTION OF A PORTION OF THE LOWER JAW 



Pl. I, Fig. ia 



The section is composed of parallel disks of bone substance situated 

 between vascular channels or clefts. The bone substance does not 

 show the presence of lacunae with their canaliculi. Very minute 

 parallel canaliculi extend across the disks from one channel or cleft 

 to another. A wave effect is given to the section by the undulating 

 forms of the clefts. This arrangement of channels in the bone sub- 

 stance produces a very fine channel circulation. At short intervals 

 within the clefts, as at C, figure i, plate i, may be seen small objects 

 from which radiate minute canaliculi presenting the appearance of 

 the canaliculi radiating from their lacunae, but these are in the vas- 

 cular clefts and not in the bone substance. 



TANGENTIAL SECTION OF A CRANIAL BONE OF THE MASCALONGE 



Pl. I, Fig. ib 



In this section are seen parallel rows of objects of various shapes 

 situated in the bone substance. Some of them are circular with dark 

 crescents on one side, while others are very irregular in shape. No 

 canaliculi extending outward from them can be seen. For this 

 reason they cannot be lacunae in the bone substance, as osteoblasts 

 occupying such lacunae would be without a blood supply. On ac- 

 count of their general circular character these objects appear to be 

 different sections of the vascular clefts of the bone and if any bone- 

 producing cells are present they must be within the vascular clefts. 



