118 THE BONES. 



particularly in walking birds, and composed, as in the mammalia, of an ilium, ischium, 

 and pubis. The ilium is consolidated with the last dorsal, the lumbar, and the sacral 

 vertebrae ; it is excavated on its internal face. The ischium partly incloses the side of 

 the pelvic cavity ; between its internal border and the external border of the ilium is an 

 orifice which replaces the great ischiatic notch. Its inferior border is united to the pubis. 

 The latter is thin and elongated, and follows the direction of the inferior border of the 

 ischium, with it circumscribing an oiial opening more or less spacious. Its inferior 

 extremity extends beyond the ischium to curve inwards towards that of the opposite side, 

 but without uniting with it. We do not, therefore, find the pelvic symphysis in birds, 

 and the pelvis is widely open below, a circumstance which favours the passage of the 

 egg through the cavity and out of the cloaca. The cotyloid cavity is perforated by an 

 opening at the bottom which traverses the bone. 



Thigh bone. — The femur is articulated inferiorly with th e patrlla, tibia, and fibula. In 

 all walking birds, like the galliuaosB, it is long and strong, as well as the rays below it. 



Leg bones. — The patella is wide and thin. The tibia terminates, below, by two con- 

 dyles separated by a groove which becomes articular behind. The fibula articulates 

 by its head with the external condyle of the femur, and is consolidated with the tibia ; 

 it never descends to the inferior extremity pf that bone. 



Tarsal bones. — The tarsus appears to be altogether absent in birds. Nevertheless 

 we may venture to consider, as a vestige of the bones of this region, a small bony nucleus 

 buried in a fibro-eartilaginous mass which glides on the posterior pulley of the tibia. 

 This nucleus represents the calcaneus of mammals. 



Metatarsal bone. — A single metatarsal bone is found in birds, articulating superiorly 

 with the inferior extremity of the tibia, and terminating inferiorly by three pulleys 

 which support the three principal digits. This bone shows in the Fowl, near its inferior 

 third, a conical process turned backwards, which serves as a base for the spur. Behind 

 its superior extremity, it exhibits another which may be considered as a consolidated 

 metatarsal bone. 



Bones of the digital region. — All the domesticated birds have four digits on the inferior 

 members : tliree principal, directed forwards, and one rudimentary, carried backwards. 

 The first, designated as internal, median, and external, articulate with the infi-rior 

 pulleys of the metatarsal bones. The internal is formed by three phalanges, the second 

 has four, and the tliird five. These phalanges are formed something like those of t- e 

 cariiivora: the last is pointed, conical, and enveloped in a horny sheath. The fouich 

 digit, or thumb, is composed of three pieces ; one of these, the first, is generally con- 

 sidered as a rudimentary metatarsal bone. It is attached by fibro-cartilaginous tissue 

 to the inner and posterior aspect of the inferior extremity of the principal metatarsal 

 bone. 



CHAPTER IV. 



THEORY OF THE VERTEBRAL CONSTITUTION OF THE SKELETON. 



In tte series of vertebratsd animals the bony pieces of the trunk bearing 

 the name of vertebrfe are those which oifer the highest degree of fixity, and 

 to which the existence or the arrangement of the others appears to be subor- 



^'dinate. This feature in organisation, recognised by E. Geoffrey Saint- 

 -Hilaire and Professor Owen, has caused these. men of science to assert that 

 ■€he type of construction of vertebrated animals is the rertebra. 



After E. Geoffrey Saint-Hilaire and Professor Owen, several German, 

 English, and French anatomists have studied the vertebral composition of 

 the skeleton; and among the works published in France on this subject must 



■ be specially noticed those of M. Lavocat.i In principle, all the writers 

 have an-ived at the same conclusions, and only differ in some few details. 



It is certain that the base of the vertebral column is formed by a series 

 of bony segments. Each of these segments is called an osieodesm, and each 



: osteodesm represents the hody or centrum of a vertebra. 



(''The distinguished anatomist and Director of the Imperial Veterinary School of 

 , Toukmse.) / vj. ui. 



