xii EXPLANATION OF THE PLATES. 



spear ; 6 an irregular mass of cement formed round the orifice 

 of the wound by the membrane of the tusk follicle, and 

 which would have closed the wound had the weapon been 

 removed. The wound inflicted has in this instance, as in 

 many others, stunted the growth of the tusk at c c, so as 

 to render the part formed after the injury narrower and 

 weaker. 



Fig. 7. A longitudinal section of a tusk in which a gun-shot wound 

 had terminated in abscess of the pulp ; a a cement ; 

 6 6 regular ivory deposited before the injury ; c c regular 

 ivory deposited after the injury ; d d irregular ivory bound- 

 ing the abscess ; e e masses of cement and irregular ivory at 

 the margin of the shot-hole. 



Fig. 8. The external aspect of a portion of a tusk, which had been 

 transversely fractured ; a a the line of fracture united exter- 

 nally by irregular masses of cement. 



Fig. 9. The internal aspect of the same portion of tusk ; a a the line of 

 fracture united by irregular ivory, a portion of which is 

 arranged in a reticular form. This reticular ivory is interest- 

 ing, as affording a natural analysis of the peculiar arrange- 

 ment of parts in the irregular ivory described in the paper. 

 Each bar of the reticular ivory is traversed longitudinally by 

 a medullary canal, from which radiate secondary canals and 

 Retzian tubes, the whole being coated with regular ivory. 

 This reticular ivory differs from the ordinary form of ossified 

 pulp, only in the greater distance between the Haversian or 

 medullary canals, so that portions of the pulp have remained 

 unossified between them. 



DEVELOPMENT OF THE SUPRA-RENAL, THYMUS, AND 

 THYROID BODIES. PLATE III. page 66. 



Fig. 1. A portion of an early embryo of the sheep. 

 a. Heart. 

 I. Lungs still in front of the intestinal tube. 



c. Wolffian body. 



d. Lateral mass of blastema, out of which is formed the supra- 



renal capsule, thymus, and thyroid. 



e. Cardinal vein. 

 /. Jugular vein. 

 g. Ductus Cuvieri. 



Fig. 2. A portion of the early embryo of the sheep, 

 a. Intestinal tube and ductus vitelli. 

 6. Liver. 



c. Omphalo-mesenteric vein. 



d. Omphalo-mesenteric artery. 



c, f. Mass of blastema on the inner side of the Wolffian body, and 



