SIGNIFICANCE OF BONE STRUCTURE. 7 



shaft of the bone. The moose (figs. 12 and 13) is a good example of the former type, 

 and indeed it is an excellent specimen of the structnrc in the quadruped. The internal 

 structure is as similar as the diUcrcnce in shape between the humerus and femur allows. 

 There is very little difference in density between the heads of these bones iu the same 

 animal. I have been able to cut only the femur of Rangifer tarandus, the caribou. The 

 sti-uctnre of the head is very dense, decidedly more so than in the femur of the moose. 

 The plates in the neck are very delicate aud near together, giving the bone rather 

 a characteristic appeai*ance. The bones of the liarteheest (figs. 14 and 15) are very strik- 

 ing. The Avails of the shaft are very thin in proportion to its diameter, and there is no 

 cancellated tissue below^ the very ends. This is pretty dense in the heads and lighter in 

 the tuberosity and trochanter. A series of plates can be traced from the inner side of 

 the shaft into the head. Both bones, but especially the humerus, present large plates 

 and bars running through empty spaces, giving very much the appearance of a bird's 

 bone. As it was known that this animal had died in a menagerie, it seems possible that 

 the bones arc pathological, but both the sheej') and the goat show in a less degree the thin 

 shaft and the absence of cancellated tissue in parts where it is found in the other un- 

 gulata that I have examined. 



Mahsupialia. In the hangaroo the humerus is much smaller than the femur, and the 

 plan not very clear. The femur (fig. IG) shows the usual plan; but these bones present 

 one remarkable peculiarity. In the ])ones hitherto described the surface of the head is 

 always of spongy tissue and the line of the epiphysis when visible cuts off a considerable 

 portion of the head. In the femur of the kangaroo the line of the epiphysis sepai-ates a 

 crust of solid bone covering the head. This crust seems precisely as compact as the 

 bone of the shaft. In the humerus there is a similar arrangement, only the outer portion 

 of the crust shows a number of small holes, an approach to spongy structure. Anxious 

 to know if this is a marsupial peculiarity, I examined the bones of the opossum and 

 found precisely the same hard cap constituted by the epiphysis in the femur, but in the 

 humerus the epiphj'sis consists of spongy tissue. 



To study the general plan of the heads of these bones we should begin with a quad- 

 ruped. We find in the humerus and femur a system of plates passing off from the outer 

 and inner walls of the shaft and forming Gothic arches at the top of the bone. The 

 head is of dense, spongy tissue, of the round-meshed pattern, into which runs a series 

 of plates from the underside of the neck. The great tubei-osity and trochanter are made 

 of looser tissue. In the former, the plan is less certain ; in the latter, it is in the main, 

 (as seen in frontal plane) a rectangular network of vertical and horizontal plates. Ex- 

 ternally there may be a series parallel with the surface. In most of the animals men- 

 tioned, this general description will apply to both humerus and femur. The head of the 

 humerus is of about the same consistency as that of the femur in ungulata, in which the 

 weight is about equally distributed between the bones, and in the seal, iu wliich neither 

 bone bears any weight. In the carnivora, in which the anterior extremity is more pre- 

 hensile, the head is lighter and this difference is still more evident iu apes and man. In 

 the apes we find a lengthening of the neck in the femur and a shorteuiug of tliat of the 

 humerus, with a corresponding change in the internal structure. 



