64 



Plate VII. 



Fig. 1. A portion of human clavicle, magnified 440 diameters, to show the bone- 

 cells and their canaliculi : the largest of the bone-cells are about g J s th, 

 the shortest about , : .v, ,1 h of an inch in length. 



Fig. 2. A portion of the transverse section of the femur of an Ostrich, magnified 

 440 diameters. An Haversian canal is seen longitudinally divided, 

 with the small bone-cells arranged in parallel lines on either side of 

 it. The length of the bone-cells is on an average about igfoth of an 

 inch. 



Fig. 3. A portion of the humerus of a Turtle (Chelonia Mydas), magnified 440 di- 

 ameters, in which the elongated bone-cells with numerous canaliculi 

 are well exhibited : the length of these bone-cells varies from ^th to 

 the gjjth of an inch. 



Fig. 4. A portion of the lower jaw of a Conger Eel, magnified 440 diameters : the 

 bone-cells are neither so long nor so broad as those of the Turtle, but 

 the canaliculi are larger and less numerous. The longest bone-cell in 

 this specimen is 3 J 3 th, the shortest t^th of an inch. 



Fig. 5. A portion of the cranium of a Menopome, magnified 440 diameters, show- 

 ing the large size of the bone-cells and the canaliculi : although many 

 of the cells are not so long as those of the Turtle, they are nevertheless 

 nearly twice as broad. The length of the cells varies from the jjjth to 

 the ^th of an inch. 



Fig. 6. A portion of the cranium of the Siren (Siren lacertina), magnified 440 di- 

 ameters. The bone-cells in this animal are the largest known ; they 

 are quite as long as those of the Menopome, and are much broader. 

 Some of them are as much as the 3 £ th of an inch in length by the j^th 

 in breadth. 



Plate VIII. 



Fig. 1. A portion of the scale of the Lepidosteus osseus, which exhibits the quad- 

 rate form of bone-cell, with few canaliculi, which is generally found in 

 thin plates of bone of fishes. 



Fig. 2. A small portion of bone, taken from the exterior of the shaft of the hu- 

 merus of a Pterodactyle, which exhibits the elongated bone-cells 

 characteristic of the higher orders of Reptilia. 



Fig. 3. A transverse section of the spine of a Silurus, which exhibits numerous 

 branching tubes or canals, like those of teeth, but no bone-cells. 



Fig. 4. A horizontal section of a scale or flattened spine from the skin of a Trygon 

 or Sting Ray, which exhibits large Haversian canals, with numerous 

 wavy parallel tubes, like those of dentine, communicating with them. 

 It will be noticed that this specimen shows, besides these wavy tubes, 

 numerous bone-cells whose canaliculi communicate with the tubes, as 

 in many specimens of dentine. 



Fig. 5. A portion of the base of the cranium of a Lepidosiren (Lepidoxiren annectens, 

 Owen), which shows two forms of very large bone-cells, similar to those 

 in the Menopome and Siren and other perennibranchiate Reptilia. 



Fig. 6. A portion of the base of the cranium of a Lepidosiren, magnified 95 di- 

 ameters, which exhibits both the elongated and the quadrate form of 

 bone-cells, for the purpose of comparison with those of the Menopome 

 and Siren, in Plate vii. figs. 5 and 6, which are similarly magnified. 



