228 OSTEOLOGY. 



from eighteen to twenty. Dixey (Proc. Roy. Soc. xxx. and xxxi.) has pointed out that 

 the primary centre in the distal phalanges commences to ossify in the distal part of 

 the bone rather than towards the centre of the body. This observation has been 

 confirmed by Lambertz, who further demonstrates the fact that ossification commences 

 earlier in the distal phalanges than in any of the other bones of the hand. Of the 

 other phalanges, those of the first row, beginning with that of the third finger, next 

 ossify, subsequent to the appearance of ossific centres in the shafts of the metacarpal 

 bones, whilst the second or middle row of the phalanges is the last to ossify about 

 the end of the third month. Sewell has recorded a case in which the proximal phalanx 

 had a distal as well as a proximal epiphysis. 



Ossa Sesamoidea. 



Two little oval nodules (sesamoid bones), which play in grooves on the volar 

 aspect of the articular surface of the head of the first metacarpal bone, are constantly 

 met with in the tendons and ligaments of that metacarpo-phalangeal articulation. 

 Similar nodules, though of smaller size, are sometimes formed in the corresponding 

 joints of the other digits, more particularly the index and little finger ; as Thilenius 

 has pointed out (Morph. Arbeiten, vol. v.), these are but the persistence of cartilaginous 

 elements which have a phylogenetic interest. 



THE BONES OF THE INFERIOR EXTREIYIITY. 



THE PELVIC GIRDLE AND THE PELVIS. 



The pelvic girdle is formed by the articulation of the two hip bones with 

 the sacrum dorsally, and their union with each other ventrally, at the joint called 

 the symphysis pubis. 



Os Coxae. 



The hip bone (os coxae) (O.T. innominate) is the largest of the " flat " bones of 

 bhe skeleton. It consists of three parts the os ilium, the os ischium, and the os pubis 

 primarily distinct, but fused together in the process of growth to form one large 

 irregular bone. The coalescence of these elements takes place in and around the 

 acetabulum, a large circular articular hollow which is placed on the lateral side of the 

 bone. The expanded wing-like part above this is the os ilium ; the stout V-shaped 

 portion below and behind it constitutes the os ischium ; while the <-shaped part to 

 the medial side, and in front and below, forms the os pubis. The two latter portions 

 of the bone enclose between them a large aperture of irregular outline called the 

 foramen obturatum (obturator foramen), which is placed in front and below, and to 

 the medial side of the acetabulum. 



The ilium, almost a quadrant in form, consists of an expanded plate of bone, 

 having a curved superior border, the crista iliaca (iliac crest). Viewed from the 

 side, this forms a curve corresponding to the circumference of the circle of which 

 the bone is the quadrant ; viewed from above, however, it will be seen to display 

 a double bend convex anteriorly and laterally, and concave posteriorly and 

 laterally. The iliac crest is stout and thick, and for descriptive purposes is 

 divided into a labium externum (external lip), a labium internum (internal lip), and 

 an intermediate surface (linea intermedia), which is broad behind, narrowest about 

 its middle, and wider again in front. About 2 \ inches from the anterior extremity 

 of the crest the external lip is usually markedly prominent and forms a projecting 

 tubercle, which can readily be felt in the living. Attached to these surfaces and 

 lips anteriorly are the muscles of the flank, whilst from them posteriorly the 

 latissimus dorsi, quadratus lumborum, and sacro-spinalis muscles derive origins. 

 The crest ends in front in a pointed process, the spina iliaca anterior superior 

 (anterior superior iliac spine). To this the lateral extremity of Poupart's inguinal 

 ligament is attached, as well as the sartorius muscle, which also arises from the 

 edge of bone immediately below it, whilst from the same process and from the 



