34 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 35 



111 a senile Haversian system, at tlie beginning of tlie process, the lamella 

 around the Haversian canal becomes dark from a deposit of inorganic grannies. 

 This deposit intensifies the clearness of the serrated edges and cement. The 

 granules increase as the process goes on, involving lamella after lamella, until 

 the whole system is opaque and black. After the lamellae have reached this 

 stage they are gradually broken down into amorphous particles which drop 

 into the Haversian canal and are removed by the blood vessels. The lamellae 

 of adjoining systems pass through similar processes. The inter-Haversian 

 lamellte follow and a cavity is formed, which in the section appears as a space. 

 This process continues with a greater or lesser rapidity until the bone, reduced 

 in dimensions and weight, remains as a mere shell of its normal condition 

 (pi. 34, figs. 423-426). 



In plate 29, figui-e 381, these changes may be observed. Haversian sys- 

 tems in different stages of senility are most numerous in the anterior and 

 outer walls and in the middle portion of the shaft of the bone. The systems 

 may be in pretty good condition elsewhere or, in extreme cases, granular de- 

 posits of ditTerent degrees of intensity may be present in most of them. The 

 internal circumferential lamellae remain in a fragmentary form. The essential 

 change, therefore, is primarily in the Haversian system. 



The changes which occur in senility may be summarized, as follows : 



1. Dissociation of the organic and inorganic constituents of the lamelhi> 

 around the Haversian canals. 



2. Deposit of inorganic granules in the lamellae around the Haversian 

 canals. 



3. Gradual extension of the inorganic deposit toward the periphery of the 

 Haversian systems and opacity of tlie lamellae. 



4. Absorption and disappearance of the granular lamelhe from the Ha- 

 versian canal outward. 



5. Widening of the Haversian canals and thinning of tlie walls of the 

 Haversian system. 



6. Disappearance of the Haversian systems and formation of irregular 

 sjiaces. (Deposit of salts in the walls of degenerating vessels.) 



7. Decrease in the weight of the bone. 



VT. AMPHIBIANS 



Tbc study begins with llic aiiiphibiaiis. 'fhirty-iiine rciiiora were exaniined. 



Genehal Chauacteh or the P"'emuk 



Tlie femora of these animals are generally small. They vary to a con- 

 siderable degree in shape. Some sections are triangular, some elliptical, some 



