92 



Reviews. 



69 



takes place. The top of the pedicle has now become very hard and 

 non-vascular, and the skin overgrows it. 



The surprising rapidity of growth of the antler is a very remarkable 

 feature. In some of the larger species, according to Flower, antlers may 

 be produced which weigh more than all the rest of the skeleton, and yet 

 the actual period of growth is only about three months. The author 

 has observed nuclear budding to take place in the osteoblasts of the growing 

 antler, in addition to the ordinary mitotic division, and suggests that 

 this occurrence may account for the great augmentation in the rate of 

 growth of the bone. There is a correspondingly rapid growth of the 

 " velvet " to keep pace with the growing bone. The velvet is a highly 

 vascular structure, arising by proliferation of the cells of the skin around 

 the pedicle, and completely covering the bony antler as a true living 

 skin with glands, hair-follicles and hairs. 



A detailed account is given of the histological phenomena accompanying 

 the processes of growth and shedding. The osteoblasts are described 

 as arising in an undifferentiated mesodermal syncytium, not from a 

 preformed connective-tissue or periosteal layer, as usuall}^ held. A similar 

 origin has been observed by the author in human and other bones, and this 

 view seems to be on a much more satisfactory basis than the theory of 

 periosteal or connective-tissue origin of the osteoblasts. ^ No periosteum 

 appears in the growing antler, the dermis lying immediately over the 

 living bone. 



A definite form or type of cell is recognised in the mature osteoblast 

 in the antler, and osteoblasts of bone from various other sources are 

 stated to exhibit the same characteristic form. This constitutes an 

 important advance upon the usual opinion that the osteoblast is definable 

 by function only, and not by any special histological character. 



An account is given of the methods by which bone is formed by the 

 osteoblasts. The two commonly recognised types of bone-formation — 

 traditionally " intramembranous " and " intracartilaginous " — are 

 described respectively as " direct " and " indirect " methods of ossifi- 

 cation. In each case the origin of the osteoblast is apparently the same, 

 but in the latter the development of the mature stage is delayed, and a 

 matrix of cartilage formed. When ossification is about to commence, 

 the osteoblast, which had temporarily assumed the role of " cartilage- 

 cell," develops into the typical mature form, and commences the deposition 

 of bony tissue. The cartilaginous matrix disintegrates, and the ground 

 substance of bone, ossein, takes its place. Calcium salts are deposited, 

 and the characteristic trabecular formation of growing " cartilage-bone " 

 appears. In the direct method of ossification, the osteoblasts early attain 

 their typical form, and at once commence the deposition of bone. Both 

 methods are in operation simul .aneously in the antler, but the indirect 

 method predominates. These facts all tend to support the view that 

 the periosteum is not a bone-forming organ, as generally stated, but 



* Cf. Rendle Short: "The New Physiology." 1920. Chap. vii. 



