IOWA ACADEMY OF SClEiVCES. 117 



"The blood supply of the peridental luerubraue is very bountiful in the 

 young subject. The larger arteries enter the alveolus mostly at the apical 

 space, or rather one or two vessels enter here and immediately break up 

 into smaller ones. One or two of these enter the root caual to supply the 

 pulp of the tooth, while the others, from four to six or eight, pass down 

 along the sides of the root to supply the peridental membrane. In their 

 passage down the membrane these divide into many branches, a consider- 

 able number of which enter the haversian canals of the alveolar wall or 

 receive branches from that source."" My own sections convey a somewhat 

 different impression. By far the greater number of arteries enter the 

 alveolus in the spaces between the roots, of molars, and none of these, so 

 far as I can discover, go directly to the root canal and thence to the pulp. 

 A very large number of vessels enter the peridental membrane from the 

 entire extent of the alveolus. 



Dr. Black seems to have drawn his conclusions largely from sections of 

 teeth of the lower animals, such as the sheep, dog, cat and pig. Indeed, I 

 can find no one who seems to have made a special study of injected human 

 teeth ground down in situ. The extreme difficulty of securing suitable 

 material for such investigations may account for this fact. 



From the above quotations, which give all that is said on the subject by 

 a number of our best and most recent authorities, it is evident that they 

 understand the blood to be supplied to the teeth in the following manner: 



The internal maxillary and inferior dental arteries supply the teeth of 

 the upper and lower jaws by giving oS a branch to each root, the branch 

 entering by a single aperture at the apex of the root. We are also given to 

 understand, although detinite statements seem painfully deficient, that the 

 branch which supplies each root passes from the main artery (internal max- 

 illary or inferior dental), directly through the peridental membrane, and 

 thence through the single apical foramen to the pulp. The present writer 

 considers that he has demonstrated an essentially different method of sup- 

 plying the blood to the teeth; at least of the domestic cat and the rat. The 

 points of special importance are: 



First. The inferior dental artery is not a single vessel; on the contrary, 

 after entering the inferior dental foramen, it divides, within the canal, and 

 the divisions anastomose and redivide in the most irregular and perplexing 

 manner. 



Second. Thei'e is nothing at all resembling the single branches of this 

 artery which are supposed to be given off to supply each root; on the con- 

 trary, by far the largest and most numerous branches of this artery pass 

 into the alveolar spaces between the roots of the teeth, and then break up 

 into a maze of small vessels, most of which ultimately pass into the peri- 

 dental membrane, considerably above the apex of the root. 



Third. No vessels, so far as my series of sections shows, pass directly 

 through the peridental meml)rane below the apex of the root, and thence 

 upward into the pulp. On the contrary, a multitude of vessels enter the 

 peridental membrane throughout its extent and pass downward toward the 

 apices of the roots, where they enter foramina, through which the pulp is 

 reached. The blood is thus distributed, first to the membrane, which is 

 exceedingly vascular, then conducted by vessels in the membrane to the 

 apices of the roots. 



'Periosteum and peridental membrane, Black, p. 85. 



