242 



THE SKELETON. 



the cancel]! being strongest and having a more accurately perpendicular course, 

 above the condyles. 



Articulations. With three bones : the os innominatum, tibia, and patella. 

 Development (Fig. 173). The femur is developed by five centres ; one for the 

 shaft, one for each extremity, and one for each trochanter. Of all the long 

 bones, except the clavicle, it is the first to show traces of ossification; this 



commences in the shaft, at about the 



Fig. 173. Plan of the Development of the fifth week of foetal life, the centres 

 Femur. By Five Centres. of oss ifi cat i on j n the epiphyses ap- 



pearing in the following order: First, 

 in the lower end of the bone, at the 

 ninth month of fcetal life ; from this 

 the condyles and tuberosities are 

 formed; in the head, at the end of 

 the first year after birth ; in the 

 great trochanter, during the fourth 

 year ; and in the lesser trochanter, 

 between the thirteenth and four- 

 teenth. The order in which the epi- 

 physes are joined to the shaft is the 

 reverse of that of their appearance ; 

 their junction does not commence 

 until after puberty, the lesser tro- 

 chanter being first joined, then the 

 greater, then the head, and, lastly, the 

 inferior extremity (the first in which 

 ossification commenced), which is 

 not united until the twentieth year. 

 Attachment of Muscles. To the 

 great trochanter: theGluteus Medius, 

 Gluteus Minimus, Pyriformis, Obtu- 

 rator Internus, Obturator Externus, 

 Gemellus Superior, Gemellus Infe- 

 rior, and Quadratus Femoris. To the 

 lesser trochanter: the Psoas Magnus, 

 and the Iliacus below it. To the 



shaft, its posterior surface: the Yastus Externus, Gluteus Maximus, short 

 head of the Biceps, Yastus Internus, Adductor Magnus, Pectineus, Adductor 

 Brevis, and Adductor Longus ; to its anterior surface : the Crureus and Sub- 

 crureus. To the condyles : the Gastrocnemius, Plantaris, and Popliteus. 



The Skeleton of the Leg consists of three bones : the Patella, a large sesa- 

 moid bone, placed in front of the knee; and the Tibia, and Fibula. 



THE .PATELLA. (Figs. 174, 175.) 



The Patella is a flat, triangular bone, situated at the anterior part of the 

 knee-joint. It resembles the sesamoid bones, from being developed in the 

 tendon of the Quadriceps Extensor, and in its structure, being composed 

 throughout of dense cancellous tissue ; but it is generally regarded as analo- 

 gous to the olecranon process- of the ulna, which occasionally exists as a sepa- 

 rate piece, connected to the shaft of the bone by a continuation of the tendon 

 of the Triceps muscle. 1 It serves to protect the front of the joint, and increases 



1 Professor Owen states, that, " in certain bats, there is a development of a sesamoid bone 

 in the biceps brachii, which is the true homotype of the patella in the leg," regarding the ole- 

 cranon to be homologous, not with the patella, but with an extension of the upper end of the 

 fibula above the knee-joint, which is met with in some animals. (" On the Nature of Limbs," 

 pp. 19, 24.) 



Joins SJta,ftatZ0*t!-. 



