BOB- WHITE— BONE 47 



Ortolan. Its good qualities have been described at length by Alex- 

 ander Wilson, Nuttall, and Audubon, to say nothing of more recent 

 writers on North-American ornithology, and to those authors must 

 reference be made for its description and an account of its habits. 

 From the purely scientific point of view the form is one of consider- 

 able interest, as it seems to connect the Emherizidse (Bunting) 

 with the Ideridse (Grackle, Icterus) ; and, though generally con- 

 sidered to belong to the latter, is rather a divergent member of 

 that Family. It is a bird that performs vast migrations, breeding 

 as high as lat. 54° N., and in winter visiting the Antilles and 

 Central and South America as far as Paraguay. 



BOB- WHITE, a nickname of the Virginian QuAiL, Ortyx vir- 

 ginianus, aptly bestowed from the call-note of the cock. 



BONE or osseous tissue consists of phosphate and carbonate of 

 lime, salt, and a few other earthy substances. Hollow bones contain 

 marrow, a fatty substance with delicate connective tissue, except 

 where it has been driven out by the penetrating AiR-SAUS. On 

 the surface of a bone, covered by a fibrous membrane, the periosteum, 

 there open small, often microscopic, holes, Avhich as " Haversian 

 Canals " are continued through the walls of the bone into larger spaces 

 or cancelli, and ultimately into the marrow cavity. These render 

 possible the entrance of blood-vessels, air-cells, and nerves. Bones 

 which have their entire substance or diploe between the outer and 

 the inner lamella filled with cavities and cancelli are called cancellated 

 or spongy ; this is especially the case in the bones of the head of 

 Owls, and to an enormous extent in the " horn " of the Hornbills. 

 The bony substance forms consecutive layers around the Haversian 

 canals. The layers themselves contain numerous irregular lacunae, 

 formerly but wrongly called bone -corpuscles, from w^hich radiate 

 numerous extremely fine canaliculi ; these communicate with those 

 of neighbouring lacunae and with the Haversian canals, securing 

 thus access of blood and lymph to any part of the bone. 



Bone is never directly formed out of the indifierent embryonic 

 tissue, it always passes through a stage of connective tissue. If 

 this tissue ossifies directly, it becomes a primary or membrane 

 bone ; if the tissue is cai-tilage and finally supplanted by bony 

 tissue, the latter forms a secondary or cartilage bone. Most of the 

 bones of a bird's skeleton pass during their development through 

 such a cartilaginous stage. Membrane bones are principally some 

 of those forming the cranium, as the parietal, frontal, maxillae, and 

 vomer. Bones which are developed in tendons by direct ossification 

 are termed sesamoid bones, as the brachial and the crural patella. 

 Either kind of bone can ossify from various centres, but these 

 " centres of ossification " do not necessarily indicate that the bone 

 in question is composed of a number of originally separate bones. 



