4 
The Bulletin 
der-like structures located at tlie anterior thoracic region, others at the 
diaphragmatic and abdominal regions, and these send extensions into 
the bones. 
Studying more minutely the structure of bone, it is found that it 
nearly always develops from a connective tissue foundation. The in¬ 
organic substance of the hone is compressed in or between the fibers of 
connective tissue, while the cells of the latter are transformed into bone 
cells. Between the fibers are uncalcified bone cells, each of which rests 
in a cavity of the matrix called a lacuna. 
Primarily, bone consists of a single thin lamella, its later complicated 
structure being produced by the formation of new lamellae in apposi¬ 
tion to the first. During its development the bone becomes vascularized 
and the vessels are inclosed in especially formed canals, known as haver- 
sian canals. 1 
The bone cells have processes that anastamose with the processes of 
other cells. They lie in special canals known as canaliculi. 
Appearance of Transverse Section of Bone 
The appearance presented by a transverse section of a long hone is 
as follows: In the center there is a large cavity which in fetal and 
early chickhood nearly always contains marrow, hut later such bones 
as the humerus contain air spaces. The periphery of the bone is cov¬ 
ered with a dense connective tissue membrane, the periosteum. In the 
young this membrane may be divided into three layers, the outer con¬ 
sisting mainly of rather coarse white fibrous tissue; the middle, fibro- 
elastic tissue, and the inner, the osteogenic layer. The inner membranous 
layer is vascular and rich in cellular elements. In the adult bird 
the osteogenic layer has practically disappeared, leaving here and there 
a few of its cells, while the fibro-elastic layer is correspondingly thicker. 
A large number of haversian canals containing blood vessels, best ob¬ 
served on transverse section, are found in compact bone tissue. Lamellae 
of hone are plainly visible throughout the ground substance and are 
arranged in the following manner: 
There is a set of lamellae extending parallel to the external surface of 
the bone, and another set similarly arranged around the inner marrow 
or air cavity. There are the so-called fundamental lamellae — known 
also as periosteal and marrow lamellae, or outer and inner circumfer¬ 
ential lamellae. 2 Around the haversian canals are concentrically ar¬ 
ranged lamellae, forming systems of haversian lamellae. There is a 
system of interstitial lamellae wedged in between the haversian system 
of lamellae. Scattered between the lamellae are found the spaces known 
as lacunae, containing hone cells. It is probable that all lamellae are in 
more or less direct communication with each other by means of fine 
canals or canaliculi. The canaliculi of the haversian lamellae of bone 
